* Add envoy metrics service protos

This patch imports protos from envoyproxy/data-plane-api and
prometheus/client_model to enable metrics service service feature in
SkyWalking OAP.
Signed-off-by: NDhi Aurrahman <dio@tetrate.io>

* Add Envoy related docs
Signed-off-by: NDhi Aurrahman <dio@tetrate.io>

* Update the LICENSE to include new protos license

From:
- envoyproxy/data-plane-api
- prometheus/client_model
Signed-off-by: NDhi Aurrahman <dio@tetrate.io>

* Add a complete config.yaml example
Signed-off-by: NDhi Aurrahman <dio@tetrate.io>

* Add note on Envoy dynamic config
Signed-off-by: NDhi Aurrahman <dio@tetrate.io>

* Add protoc-gen-validate license
Signed-off-by: NDhi Aurrahman <dio@tetrate.io>

* Add samples
Signed-off-by: NDhi Aurrahman <dio@tetrate.io>

* Make CI and license right.

* Update README.md

@dhi typo :P

* Update README.md

Another typo :P

* Delete metrics.json

metrics.json is included in identify.json and not be linked in document.

* [maven-release-plugin] prepare release v6.0.0-GA

* [maven-release-plugin] prepare for next development iteration

* Lock oracle and resin plugins version.

* Move resin and oracle plugin to openskywalking

* Restore submodule active.

* Add another submodule active command.

* Remove the wrong test cases in release and fix some doc issues.

* [maven-release-plugin] prepare release v6.0.0-alpha

* [maven-release-plugin] prepare for next development iteration

* Fix some doc

* Buffer stream.

* Buffer file reader.

* Buffer library performance test and functional test successfully.

* Fixed the code merge mistake.

* SkyWalking's trace receiver implementation.

* SkyWalking's trace receiver implementation.

* Delete collector module.

* Register start up.

* Service inventory register test success.

* Receiver, aggregate, server finished.

* Cluster module implementation finished.

#1009

* [maven-release-plugin] prepare release apm-5.0.0-alpha

* [maven-release-plugin] prepare for next development iteration

Fix assmbly for mvn clean install -Papache-release and update version to SNAPSHOT for SNAPSHOT release.