Release v1.6.0-beta.1

[csuzhangxc]

This is an issue tracking the tidb-operator v1.6.0-beta.1 release.

Previous:

• 5509

Pending PRs:

TODO:

• [x] Update default version of TiDB Operator #5591
• [x] Update TiDB version and tools version if necessary #5591
• [x] Update the TiDB version and tools version in docs-tidb-operator repo https://github.com/pingcap/docs-tidb-operator/pull/2520
• [x] Update release notes https://github.com/pingcap/docs-tidb-operator/pull/2519
• [x] Update Github Releases
• [x] Build and publish docker images/helm charts
• [x] Announcement (slack, email, etc.)
• [x] Update TiDB Operator version in docs-tidb-operator repo (both for dev and stable branch) https://github.com/pingcap/docs-tidb-operator/pull/2530