register and show when an LDAP user was detected as unavailable/deleted

[blizzz]

• a background job checks whether known LDAP users are still present. If not they are flagged as "deleted". Which was not recorded, was the date of the detection. This information is now recorded. (As a another db row in the preferences as the IConfig API only allows to request users for a precise value).
• For output a column/field "Detected on" to the ldap:show-remnants command was added.
• Also added was a --short-date flag to display it in "Y-m-d" format which is easier to consume for scripts that may react on it. For users that were detected earlier, the value "unknown" is shown instead.

How to test?

1. Have LDAP configured
2. Log in with one of the LDAP users.
3. Delete this user in LDAP
4. Manually check the existance of it per occ ldap:check-user $uid (beware caching)
5. Assert occ ldap:show-remnants shows this user as deleted, with a readable long time format
6. Assert occ ldap:show-remnants --short-date shows this user as deleted, with Y-m-d formatted date

[blizzz]

/backport to stable15

[blizzz]

/backport to stable14

[rullzer]

🐘

[skjnldsv]

We really need to create a all-in-one docker for ldap instead of the weird thing we have from the owncloud documentation :)

[blizzz]

rebased for CI

[MorrisJobke]

Tested and works 👍

[MorrisJobke]

1) OCA\User_LDAP\Tests\User\DeletedUsersIndexTest::testMarkAndFetchUser
Failed asserting that true is false.
/drone/src/github.com/nextcloud/server/apps/user_ldap/tests/User/DeletedUsersIndexTest.php:75

[backportbot-nextcloud]

backport to stable15 in #13372

[backportbot-nextcloud]

backport to stable14 in #13373