quickstart: Improve usability of check_db script

Adjust the check_db script to be more user friendly. This includes:
 - Mapping all the fields we have in the ui to the output of the
script.
 - Make it ask for password if not provided.
 - Make it produce a list of things to fix if they are not compliant
with
Readyset requirements.
 - Add a naive function to suggest a CIDR block for Readyset.
 - If the instance has public IP, it will suggest the public
connection type.
 - Fix the query to check the number of tables. It now matches
Readyset core.
 - Rename the script to check_db_postgres.sh to make it clear it is
for Postgres only.

Change-Id: I64a1e56e07a357a031b48516e900929b0b8e3939
Reviewed-on: https://gerrit.readyset.name/c/readyset/+/6990
Tested-by: Buildkite CI
Reviewed-by: Jason Brown <[email protected]>