Motivation:

According the feedback from the community, the e2e tests are hard for
them to understand and get them started, so this pull request aims to
rewrite the e2e tests with some improvements:

- debuggable locally, now you can run every individual case directly
inside the IDE, just like running a plain unit test.

- same functionalities of multiple counterparts share the same codes,
cases like different storages and cluster coordinators share the same
codes, easy to add more similar cases.

- the "end" now extends to the Doccker images, meaning that some bugs
like #4483 and #4471 can be more easily and early to be discovered.

- codes style and license headers are checked

Modifications:

- adopt jupeter (a.k.a junit 5), testcontainers as the new test
framework, all containers are orchestrated by docker-compose.yml,
well-known technology that developers should be familiar with.

- rewrite all test cases and verify them.

- reorganize the workflows in GitHub Actions.

Result:

- new e2e test should be easy to add.

- closes https://github.com/apache/skywalking/issues/4472

Motivation:

Review code styles with some bots automatically.

Modifications:

Set up ReviewDog in GitHub Action to review code style.

Add more check rules to checkstyle plugin.

Result:

Obvious code styles can be reviewed and commented automatically.

* Support new percentile func with new alarm and exporter for this new func.

* Fix e2e and OAL script

* Fix wrong column.

* Fix percentile bug and oal engine bug.

* Update query protocol and add percentile test case

* Support new query

* Adopt GraphQL requirement

* Fix wrong type cast.

* Fix query in H2 and ES.

* Fix docs and comments.

* Fix an e2e compile issue

* Fix javadoc issue and e2e test issue.

* Change CPM to Apdex in TTL test.

* Fix OAL for TTL e2e

* Add metrics query for service percentile.

* Fix OAL engine bug. Method deserialize is not working when more than two field types are IntKeyLongValueHashMap

* Support multiple IntKeyLongValueHashMap fields in remote. About serialize/deserialize methods.

* Fix graphql statement error in e2e.

* Fix serialize not working and add generated serialize/deserialize of percentile into test cases.

* Fix test case format

* Remove generated code test.

* Fix failed e2e test

* Use avg resp time to apdex in the TTL test.

* ADD multiple linear metrics check for endpoint in e2e cluster.

* Support `-` to represent no threshold and doc of alarm about this.

* Move break to right place.

* Fix wrong break(s)

* Fix break and add a test case for multiple values alarm.

* Fix format.

* Add more doc for this new feature and GraphQL query protocol.
Co-authored-by: NJared Tan <jian.tan@daocloud.io>
Co-authored-by: Nkezhenxu94 <kezhenxu94@163.com>

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.

* Provide Nacos dynamic configuration center implementation. fixes #2816

* Add unit tests

* Sync

* Replace pull-mode with watch-mode

* Fix ci

* Unify dependency management

* Add integration tests

* Revert unexpected changes

* Add more test cases

* Revert unexpected changes

* Suppress IDE warning

* Correctify volumes position

* Add license header

* Remove Chinese comments

* Sync

* Sync

* Sync

* Sync

* Revert unexpected changes

* Rebase on refactored code and add missing config to docker

* Fix unit test

* Revert unnecessary changes

* OAP server testing module.

#1930

* #Missing delete code.

* Receiver, aggregate, server finished.

* Cluster module implementation finished.

Module class rename to ModuleDefine, Module is the JDK9 class. It is conflict with our Module class. (#1168)

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

#346