Update security release process to reflect the last release.

Several small changes to the process to reflect the last security release 2.2.2.

• The branch for security release omits patch version security-2-2-0 -> security-2-2.
  • There could be more patches released from the same branch (e.g. 2.2.1 and 2.2.2) and the patch version 0 seems unnecessary.
• Instead of creating backporting MR for each change, we'll create backporting MR with all changes from the security release.
• We'll do backporting only after releasing the change and validating the fix is working.