Add configurable known groups

[LukasKalbertodt]

Fixes #952

Known groups are stored in the database and manipulated via CLI commands. This makes it a lot easier to script and/or add lots of groups, compared to storing them in the config file. The documentation added in one of the later commits should explain everything in detail, and the commit messages should help understand this patch. Can be reviewed commit by commit.

As usual, the last commit (configuring groups for the test deployment) is not used by this test deploy yet, but only after merging this PR. And as usual, since I couldn't easily test this, there is probably something slightly broken :P but i can just fix that after merging.

[LukasKalbertodt]

I learned a bit about Postgres extensions. In PG 12 and earlier, most extensions (including pgcrypto and hstore) require super user privileges to enable. With PG13, the concept of "trusted extensions" was added. For those trusted ones, any user with create privileges on the DB can enable them. The two extensions we use are trusted. Our documentation already mentions that in PG12 and earlier, one has to manually enable the extensions. But now I know why :D

But this makes this PR potentially breaking. I marked it with changelog:breaking just to remind us to write a note into the changelog for the next release. Otherwise it will be an annoying update for some.

For reference, on the dev DB:

tobira=# select * from pg_available_extension_versions() where name like '%pgcrypto%' or name like '%hstore%';
   name   | version | superuser | trusted | relocatable | schema | requires |                     comment                      
----------+---------+-----------+---------+-------------+--------+----------+--------------------------------------------------
 hstore   | 1.4     | t         | t       | t           |        |          | data type for storing sets of (key, value) pairs
 hstore   | 1.5     | t         | t       | t           |        |          | data type for storing sets of (key, value) pairs
 hstore   | 1.6     | t         | t       | t           |        |          | data type for storing sets of (key, value) pairs
 hstore   | 1.7     | t         | t       | t           |        |          | data type for storing sets of (key, value) pairs
 hstore   | 1.8     | t         | t       | t           |        |          | data type for storing sets of (key, value) pairs
 pgcrypto | 1.3     | t         | t       | t           |        |          | cryptographic functions

[owi92]

Good work, the commands for adding/updating/etc. the known groups are all working very well.

I noticed two things during my testing:

• db clear and db reset aren't working unless the hstore extension is manually dropped from the db first (db error: ERROR: cannot drop type ghstore because extension hstore requires it. HINT: You can drop extension hstore instead.).
• The superset detection thing in the access ui isn't using the implies field of the known_groups table entries yet, so the only groups regarded as supersets are the default ones (everyone, logged in users).

[owi92]

This doesn't use the supersets/implies entries from groups.json yet (there is a TODO for that in line 662). Do you plan to do this in a follow up PR?

[LukasKalbertodt]

Well done catching those! It should all be fixed now. The db reset thing is a new commit, everything else is amended and should be visible in the force-push-compare-button.

[owi92]

👌