Release v1.5.1

[csuzhangxc]

This is an issue tracking the tidb-operator v1.5.1 release.

Previous:

• Release v1.5.0 #5108

Pending PRs:

TODO:

• Update default version of TiDB Operator bump TiDB Operator to 1.5.1 #5344
• Update TiDB version and tools version if necessary
  • no need now until v7.1.2 released
• Update the TiDB version and tools version in docs-tidb-operator repo
  • no need now until v7.1.2 released
• Update release notes en,zh: add v1.5.1 release notes docs-tidb-operator#2458
• Update Github Releases
• Build and publish docker images/helm charts
• Announcement (slack, email, etc.)
• Update TiDB Operator version in docs-tidb-operator repo (both for dev and stable branch)
  • en,zh: bump operator to v1.5.1 docs-tidb-operator#2459
  • en,zh: bump operator to v1.5.1 for release-1.5 docs-tidb-operator#2460