Release v1.5.5

[csuzhangxc]

This is an issue tracking the tidb-operator v1.5.5 release.

Previous:

• Release v1.5.4 #5726

Pending PRs:

TODO:

• Update default version of TiDB Operator bump TiDB Operator to v1.5.5, TiDB to v7.5.5 #6040
• Update TiDB version and tools version if necessary bump TiDB Operator to v1.5.5, TiDB to v7.5.5 #6040
• Update the TiDB version and tools version in docs-tidb-operator repo en,zh: Bump tidb components to v7.5.5 docs-tidb-operator#2674
• Update release notes en,zh: add v1.5.5 release notes docs-tidb-operator#2673
• 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 if necessary) en,zh: bump operator to v1.5.5 docs-tidb-operator#2675