Fix a missing link

Here are the list of changes we made in this pull request. Top 3 are the principle changes, others are following these principles.
1. New agent and mesh report protocol. 
2. New agent header protocol. 
3. Service register, instance register and network address register have been removed permanently.
4. Service traffic, instance traffic and network alias metrics are added to replace the service, instance and network address inventory.
5. Register process has been removed.
6. Metrics stream process supports insert only mode, especially for traffic entities.
7. Metrics stream process supports no-downsampling mode for traffic entities and network alias.
8. Remove all register mechanism and cache in the java agent.
9. Remove MONTH step in GraphQL query.
10. Update UI to remove MONTH step query, the max query range is 60 days now.
11. Simplify the TTL to metrics and record. And the unit has been formatted in Day unit. No specific TTL for ElasticSearch storage.
12. Buffer mechanism of trace receiver and mesh receiver has been removed due to no register.
13. New service id, instance id and endpoint id rules, including service relation, instance relation and endpoint relation id rules.
14. Java agent support `keep tracing` mode, meaning, agent generating tracing context even the backend is unconnected/unavailable.
15. Plugin test tool up to date, in order to support new protocol.
16. Plugin tests expected data files updated.
17. E2E tests updated.
18. Telemetry of Grafana config has been merged into one.
19. Documentation updates.
20. [TBD] InfluxDB storage implementation is not available, need @dmsolr to fix later, in order to reduce the master change block by this PR.

* Add UI documentation.

* Fix

* Fix size.

* update doc version

* ref 6.x branch

* ref 6.x branch

* update doc/README.md

* remove 5.x ...

* Fixes: README.md

* Adds: new FAQ

See issues #3924, #3935, #3975

* Fixes: setup documentation

* Update README.md

* Add reference to module architecture diagrams

* Changed order of the links according to PR comment

* Add SkyWalking plugin test framework doc

* Remove Chinese.

* Add a description to the env variable, CASE_SERVER_IMAGE_VERSION

* Fix typo

* Change paragraph structure.

Update all "incubator-skywalking" to "skywalking" ,"incubator-servicecomb-java-chassis" to "servicecomb-java-chassis" correctly, and ".gitmodules" will update at #2531 (#2548)

* Replace v5 changes by a link to 5.x branch. New v6 changelog.

* Finish query doc and fix a missing field in alarm doc.

* Add link to official oal in alarm doc.

* Fix words.

* Fix some doc

* Update README.md

* Update README.md

* Update README.md

* Update README.md

* Change oal doc.

* Remove typo

* Remove document WIP tag.

* Fix few words.

* no message

* Adjust contribution guides.

Add a lot of documents. @peng-yongsheng @hanahmily . Also @hanahmily , the k8 cluster management document and deploy document need you to add.

* Fix bug stop stopSpan when not createSpan

* Fix bug stop stopSpan when not createSpan

* change the agent log level to millisecond

* add the function of the specified-agent-config

* Update README_ZH.md

* Use -D  to set the specified config path

* add docs

* update docs

* change method name

* add link

* change the function name

* change the key

* format doc

* Create Architecture.md

* Update Architecture.md

* Update Architecture.md

* Update Architecture.md

* Update Architecture.md

* Update Architecture.md

* Update README.md

Add link in menu. Also related to #1360

* Update Architecture.md

* Update Architecture.md

* Update Architecture.md

* Update Architecture.md

* Update Architecture.md

* Update Architecture.md

* Add Zipkin receiver

* support shardingjdbc database storage feature

* Reorganize incubating and optional docs.

* Refactor English documents to guide end users.

* To bring forward a way to solve Import-Project-Eclipse-RequireItems-Exception

* way to solve Import-Project-Eclipse-RequireItems-Exception

* To bring forward a way to solve Import-Project-Eclipse-RequireItems-Exception

* Required items could not be found, when import project into Eclipse.

* using markdown style to quote the errors.

* provides a optional-plugin for tracking ignores enhancement(#1203)

* trace ignore plugin config support override by system.env

* optimize the trace ignore plugin and make normalization of pom

* add AntPathMatcher and an junit test for it

* No longer rely on the spring framework

* add license at file header

* rebuild pom and rewrite README

* rebuild optional-plugins pom

* clean up useless code

* modify junit

* rewrite the ant path match logic

* rename the matcher class

* add the trace ignore plugin introduce doc to incubating features menu.

* modify the README doc.

* remove Chinese in English doc.

* remove superfluous content of EN-doc.

* Update README.md

* update faq doc

* update faq

* update faq

* Register table description.

* Update Collector-Table-Description.md

Review and update the docs

* Update Collector-Table-Description.md

* Test link.

* Update Collector-Table-Description.md

* Tables of JVM Metric related finish.

* Table description finish.

* Update Collector-Table-Description.md

* Update Collector-Table-Description.md

* Module class rename to ModuleDefine, Module is the JDK9 class.

* Revert "Module class rename to ModuleDefine, Module is the JDK9 class."

This reverts commit 097665b97ea53b27565e362d28c2e8202710f4cd.

* Modify short column name.

* Modify the description of transaction metrics.

* Add section about collector table description in readme.

* Protoc plugin fails when build

* add doc for TraceCrossThread