* Downstream command protocol example.

* Add wait seconds arguments into meta data reset command.

* Style consistent issue fixed.

* Add serialNumber arguments for agent to check if the command duplicate.

* Command separate.

* Update TraceIgnoreCommand.java

Keep TraceIgnoreCommand just named `TraceIgnore`

Add catalog to ScopeDeclaration annotation. Make the alarm adapt to it. Now more metric could go through alarm, such as JVM, CLR. (#2391)

* Add SmartSql provider components in component-libraries config

* sync SmartSql provider setting -> fix https://github.com/apache/incubator-skywalking/issues/2390

* Added elasticsearch warehouse certification support

* Add the elasticsearch service for Http Basic instructions

* Update backend-storage.md

Change document.

Fix link and add a notice

USE_QUALIFIED_NAME_AS_ENDPOINT_NAME configuration

Added 4 expressions in OAL syntax: >, <, >=, <=.

Merge remote-tracking branch 'origin/qualified-spring-mvc-endpoints' into qualified-spring-mvc-endpoints

* Rename ALarmSupported to WithMetadata

* Finish the base of exporter.

* Fix class comment.

Async core APIs in java agent

* Update powered-by.md

Change order

Update apm-sniffer/apm-agent-core/src/main/java/org/apache/skywalking/apm/agent/core/context/trace/AbstractTracingSpan.java

Fix isInAsyncMode never be set.
Co-Authored-By: wu-sheng <wu.sheng@foxmail.com>

Remove the version setting in dependencies.
Remove the scala compiler version property.