Release v1.2.1

[KanShiori]

This is an issue tracking the tidb-operator v1.2.1 release.

Previous:

• release 1.1.0 #2567
• release v1.1.1 #2775
• release v1.1.2 #2839
• release v1.1.3 #3010
• Release v1.1.4 #3140
• Release v1.1.5 #3263
• Release v1.1.6 #3380
• Release v1.1.7 #3495
• Release v1.1.8 #3616
• Release v1.1.9 #3656
• Release v1.1.10 #3754
• Release v1.1.11 #3812
• Release v1.1.12 #3919
• Release v1.1.13 #4049
• Release v1.2.0-beta.2 #3950
• Release v1.2.0-rc.1 #3998
• Release v1.2.0-rc.2 #4055
• Release v1.2.0 #4104

Pending PRs:

TODO:

• Update default version of TiDB Operator Bump operator to v1.2.1, tidb to v5.1.1 and DM to v2.0.6 #4143
• Update TiDB version and tools (may include DM) version if necessary Bump operator to v1.2.1, tidb to v5.1.1 and DM to v2.0.6 #4143
• Update TiDB version in the docs-tidb-operator repo if necessary en,zh; Bump tidb components to v5.1.1 docs-tidb-operator#1355
• Update DM version in the docs-tidb-operator repo if necessary en,zh; Bump DM to v2.0.6 docs-tidb-operator#1356
• Update release notes en, zh: add release notes for v1.2.1 docs-tidb-operator#1359
• Update Github Releases https://github.com/pingcap/tidb-operator/releases/tag/v1.2.1
• Build and publish docker images/helm charts
• Announcement (slack, email, etc.)
• Update TiDB Operator version in docs-tidb-operator repo en, zh: Bump Operator to v1.2.1 docs-tidb-operator#1363