Signed-off-by: NHongtao Gao <hanahmily@gmail.com>

* [maven-release-plugin] prepare release v8.4.0

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

* [maven-release-plugin] prepare release v8.3.0

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

* [maven-release-plugin] prepare release v8.2.0

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

* [maven-release-plugin] prepare release v8.1.0

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

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.

* Introduce Agent-Test-Tool suite

* rename term

Provide the codebase of plugin tests. Make the plugin test in the CI loop.

* Add TTL E2E test

* Add to Jenkins stage and minor bugfix

* Upgrade e2e container version

* Polish and minor fix

* Polish

* Support Gateway without agent

* Add e2e cluster tests

e2e test setup. cc @hanahmily @peng-yongsheng @IanCao @zhaoyuguang @JaredTan95 

# e2e test case
One single standalone Spring service, accessing H2 database. This service has been installed the agent. 
OAP runs in single mode with H2 storage too.

The e2e test will verify the results through GraphQL query
1. Traces exist.
2. Service/Service Instance/Endpoint exist and have expected metrics.
3. Topology exists and match expected.

* [maven-release-plugin] prepare release v6.2.0

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

* Move submodule plugin.

* Always auto-submodule

* [maven-release-plugin] prepare release v6.1.0

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

* Change keys location.

* [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

* 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.

Make agent gRPC to be a collector module.
Make agent jetty to be a collector module.
Make agent stream to be a collector module.