have a `comment` argument wherever an object is created

[hunleyd]

  From a user perspective I think it would be more convenient to have a `comment` argument wherever an object is created. To only change a comment, they need to be idempotent. At a quick glance, the argument would suit 11 modules:

• [x] postgresql_db: #646
• [x] postgresql_ext: #652
• [ ] postgresql_idx
• [x] ~~postgresql_lang~~ (deprecated)
• [x] postgresql_publication: #654
• [x] postgresql_schema: #650
• [ ] postgresql_sequence
• [x] postgresql_subscription: #655
• [ ] postgresql_table
• [x] postgresql_tablespace: #651
• [x] postgresql_user: #649 (already had the feature, uses the shared function now)
• [x] add the comment argument value to check_input(...), check across all the modules
• [x] check reset functionality in all the modules except publication for consistency
• [x] add check_mode + mogrify to set_comment, fix tests across all the modules where it makes sense

I'd say the benefit of a comment argument or postgresql_comment module over postgresql_query is that we can validate the kind of object which is commented, to avoid SQL injections. As this is part of the query syntax, not a variable, we cannot rely on psycopg2/3 variable escaping.

Originally posted by @betanummeric in https://github.com/ansible-collections/community.postgresql/discussions/352#discussioncomment-3834647

[hunleyd]

the comment argument feels like a good thing to me, it must be idempotent, of course. it can be a shared class/function

[Andersson007]

Working on it, will be updating the issue description along the way

[hunleyd]

thanks for all your efforts to get this work as far along as you did @Andersson007 !

now we just need someone to step up for the remaining three items in the description.