Add tags for the rocksdb rebase points in our repo

[udi-speedb]

We are periodically rebasing our repo on specific RocksDB releases. It would be useful to have a standard tag that will allow us:

• Easily find those rebase points
• Easily compare to / checkout such a point

The convention will be: rocksdb-[full rocksdb version number] For example, the lastest rebase (on rocksdb 8.1.1) will have the tag: rocksdb-v8.1.1

[Guyme]

Will be documented internally