otherwise characters with diacritics are ignored

backport of https://github.com/provinzkraut/cologne_phonetics/pull/2

prevent contact data from being included in debug logs

See merge request !1975

steps to reproduce:

-   set `DEBUG = False`
-   set `ADMINS` to a non-empty value
-   raise an exception in some POST handler
-   make a POST request to that view

The default logging configuration will generate a debug mail to the
addresses defined in `ADMINS`. This message contains all environment
variables, settings, GET and POST parameters, and a stack trace.

With this change, all POST parameters will be replaced by `'*********'`.

allow to search for slugs in subject admin

See merge request !1972

otherwise it is nearly impossible to find subjects based on information
from the UI

clear followup_time on participation status change

See merge request !1969

fixup 0da3e65d

fix: do not display "unreachable" warning when guardians have been blocked due to privacy level

See merge request !1968

Revert "rm datetime attributes"

See merge request !1965

This reverts part of commit 4d0cb2d1.

These attributesare used in appointments-form.js

refactor: mv base_template from context to view

See merge request !1964

simplify get_success_url for stay on same view

See merge request !1963

perf: avoid looping through all subjects in contact form

See merge request !1959

mention AUTH_LDAP_FIND_GROUP_PERMS in example settings

See merge request !1952

Revert "CI: Cache multi stage build"

See merge request !1955

This reverts commit 2926225a.

This did not improve build time (1:27 -> 1:40).

CI: cache multi stage build

See merge request !1951

update-deps: django-mfa3 security release

See merge request !1950

changelog pseudonyms subject export

See merge request !1948

I18n

See merge request !1947

pseudonyms in subject export

See merge request !1946