In this PR, I have:
- removed the docs for Manager (including the sources for Manager 2.1 and the upgrade guides).
- added redirects to https://manager.docs.scylladb.com/.
- replaced the internal links with external links to https://manager.docs.scylladb.com/.
Closes#11162
* github.com:scylladb/scylladb:
doc: update the link to fix the warning about duplicate targets
Update docs/kb/gc-grace-seconds.rst
Update docs/_utils/redirects.yaml
doc: update the links to Manager
doc: add the link to manager.docs.scylladb.com to the toctree
doc: remove the docs for Manager - the Manager page, the guide for Manager 2.1, Manger upgrade guides
doc: add redirections from Manager 2.1 to the Manager docs
doc: add redirections to manager.docs.scylladb.com
38d0db4be5