document undocumented settings, document settings vs. environment variables

[simonLeary42]

Many environment variables and settings are used but not documented. I have added these settings to the docs, but I haven't actually added descriptions for them (except project_openldap). Some of these appear as though they were left out intentionally, so I have marked them as "internal use only".

The documentation is unclear about which settings are appropriate for local_settings.py and which are appropriate for environment variables. I have specified for each setting whether it can be used for each. It's very inconsistent, so I think this is valuable information.

There are some settings / env vars which are not referenced anywhere in the coldfront code base, as far as I can tell:

PLUGIN_AUTH_LDAP
PLUGIN_AUTH_OIDC
PLUGIN_FREEIPA
PLUGIN_IQUOTA
PLUGIN_LDAP_USER_SEARCH
PLUGIN_PROJECT_OPENLDAP
PLUGIN_SLURM
PLUGIN_XDMOD

I marked these with question marks in the docs because I don't understand how they work. Please advise.

To ensure that the documentation stays comprehensive in the future, I added a CI workflow that uses regular expressions to check that all settings and environment variables used are present in docs/pages/config.md. This is documented in CONTRIBUTING.md as a new convention.

I also added a CI workflow that uses regular expressions to check that all settings and environment variables present in docs/pages/config.md are actually used. The question mark variables mentioned above are excempt from this check, as well as DB_URL which I assume is known by Django proper.

If #815, is going to be addressed, it should be done first and then I can remove that setting from here as well.

Future work:

• to make Coldfront's behavior more predictable, I think some standards need to be set like "all environment variables must also have corresponding settings" or "all settings must also have corresponding environment variables"
  • the files /tmp/settings.txt and /tmp/envvars.txt in the CI workflow would prove most useful for enforcing such a standard
• and of course the blank cells in the tables in the docs need to be filled out soon