write full service documentation for donate-neo

we have docs on donate-review in our wiki, but no docs for donate itself. let's throw as much shit as we can in the wiki, following the service template.

this was driven by the alerting work (#75 (closed)) which need a playbook, and i have nowhere to put that right now.

bits missing while reviewing the template:

• how do we run the test suite or test that things are still working after an upgrade? (@stephen) also cross-ref with @mattlav's checklist, see also #14 (closed) (done in tpo/tpa/wiki-replica!53 (merged))
• pager playbook: , how do we start debugging issues like high latency or exceptions? where do we look? how do we profile the app? (@stephen)
• storage: which data is stored in the sqlite database? so far i have "information about user sessions, users, logs, and CAPTCHA tokens" (@stephen)
• authentication: do we have users in django, is the admin interface visible? (@stephen)
• also authentication: document the CAPTCHA system, see also #51 (@stephen)
• queues: describe "queues", e.g. how redis is used, (@anarcat drafted a first, @stephen needs to review/expand)
• review the service/crm docs as well (@anarcat, pinged @mathieu about CRM-specific docs updates in https://gitlab.torproject.org/tpo/web/civicrm/-/issues/139)
• review and integrate design details from donate-static#107 (closed) (@anarcat)
• merge https://gitlab.torproject.org/tpo/web/donate-neo/-/issues/20 into the "other alternatives" section (@anarcat)

stuff that can wait after launch:

• design: confirm whether we diverged from the original design from @kez and how (@stephen)
• installation: donate-01 installation instructions, including backup/restore procedure for the main site (@lavamind )
• upstream @stephen can i name you as our consultant in "maintainer" or should you be our "upstream"?