[SPDK] SPDK 21.01 LTS backporting

Hi all,

Before each SPDK release a hashtag for patches is used to focus on the ones that should make it into particular release. During code freeze window, such patches are merged to latest SPDK and backported to a branch for the particular release.
Particular hashtag was in use for short period of time, targeting specific release.
This works quite well for the quarterly releases, since patches are current and actively worked on by the submitter. Meanwhile for LTS maintenance releases, such patches had to be identified and backported despite being submitted weeks or months prior.

To provide better support for SPDK 21.01 LTS - I'd like to propose using '21.01' hashtag throughout the year. Any patch that resolves critical issue and should find it's way into the LTS can be marked with this hashtag.
Shortly after merging to the latest SPDK, a backport will be submitted to the 'v21.01.x' branch for review.

Benefits would include always up to date 'v21.01.x' maintenance branch. Along with quicker identification and less risk of omissions of required changes.

I'd like to encourage submitters and reviewers to use '21.01' hashtag for any patch fit for the LTS.
Please let me know if you have any questions or suggestions.

Thanks,
Tomek