Add changelogs of 6.2.0 (#2964)

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Release Notes.

6.2.0

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#### Project

* ElasticSearch implementation performance improved, and CHANGED totally. Must delete all existing indexes to do upgrade.

* CI and Integration tests provided by ASF INFRA.

* Plan to enhance tests including e2e, plugin tests in all pull requests, powered by ASF INFRA.

* DataCarrier queue write index controller performance improvement. 3-5 times quicker than before.

* Add windows compile support in CI.

#### Java Agent

* Support collect SQL parameter in MySQL plugin.[Optional]

* Support SolrJ plugin.

* Support RESTEasy plugin.

* Support Spring Gateway plugin for 2.1.x

* TracingContext performance improvement.

* Support Apache ShardingSphere(incubating) plugin.

* Support `span#error` in application toolkit.

* Fix OOM by empty stack of exception.

* FIx wrong cause exception of stack in span log.

* Fix unclear the running context in SpringMVC plugin.

* Fix CPU usage accessor calculation issue.

* Fix SpringMVC plugin span not stop bug when doing HTTP forward.

* Fix lettuce plugin async commend bug and NPE.

* Fix webflux plugin cast exception.

* [CI]Support `import` check.

#### Backend

* Support time serious ElasticSearch storage.

* Provide dynamic configuration module and implementation. Slow SQL threshold supports dynamic config today.

* Dynamic Configuration module provide multiple implementations, DCS(gRPC based), Zookeeper, Apollo, Nacos.

* Provide P99/95/90/75/50 charts in topology edge.

* New topology query protocol and implementation.

* Support Envoy ALS in Service Mesh scenario.

* Support Nacos cluster management.

* Enhance metric exporter. Run in increment and total modes.

* Fix module provider is loaded repeatedly.

* Change TOP slow SQL storage in ES to Text from Keyword, as too long text issue.

* Fix H2TopologyQuery tiny bug.

* Fix H2 log query bug.(No feature provided yet)

* Filtering pods not in 'Running' phase in mesh scenario.

* Fix query alarm bug in MySQL and H2 storage.

* Codes refactor.

#### UI

* Fix some `ID is null` query(s).

* Page refactor, especially time-picker, more friendly.

* Login removed.

* Trace timestamp visualization issue fixed.

* Provide P99/95/90/75/50 charts in topology edge.

* Change all P99/95/90/75/50 charts style. More readable.

* Fix 404 in trace page.

#### Document

* Go2Sky project has been donated to SkyAPM, change document link.

* Add FAQ for ElasticSearch storage, and links from document.

* Add FAQ fro WebSphere installation.

* Add several open users.

* Add alarm webhook document.

All issues and pull requests are [here](https://github.com/apache/skywalking/milestone/33?closed=1)

6.1.0

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