Summary:
This diff adds a yb-admin command for the `AreNodesSafeToTakeDown` command, which checks
whether it is possible to take down a set of nodes without losing quorum (under-replication is
allowed).

The syntax is:
```
yb-admin are_nodes_safe_to_take_down <tserver_uuids|NONE> <master_uuids|NONE> <follower_lag_bound_ms>
```
Jira: DB-17643

Test Plan: `./yb_build.sh --cxx-test yb-admin-are-nodes-safe-test`

Reviewers: hsunder, anijhawan

Reviewed By: hsunder, anijhawan

Subscribers: anijhawan, ybase

Differential Revision: https://phorge.dev.yugabyte.com/D45486