Fixes #36699 - Reject invalid expiration dates for PATs

[adamruzicka]

Previously invalid dates were silently discarded, resulting into PATs being created without expiration dates.

[theforeman-bot]

Issues: #36699

[ekohl]

Small nits to use a more precise assertion, but otherwise 👍

[pondrejk]

Checked using the related test in robottelo automation against patched stream build:

pytest tests/foreman/cli/test_user.py::TestPersonalAccessToken::test_negative_personal_access_token_invalid_date
============================================= test session starts =============================================
                                                             
tests/foreman/cli/test_user.py .                                                                        [100%]

============================================= 1 passed in 28.59s ==============================================

[ofedoren]

Don't we translate the errors?

[adamruzicka]

Right, fixed

[ofedoren]

Thanks, @adamruzicka, checked with hammer.
Before:

$ hammer user access create --user user --name name --expires-at 2021-12-12
Personal access token [name] created:
cMDyzdVNTMpOG8FI1cZALw

$ hammer user access create --user user --name name --expires-at 2024-44-44
Personal access token [name] created:
iavA1FNNMtoSQkvV8TtoZA

After:

$ hammer user access create --user user --name name --expires-at 2021-12-12
Could not create personal access token:
  Expires at cannot be in the past
  
 $ hammer user access create --user user --name name --expires-at 2024-44-44
Could not create personal access token:
  Expires at Could not parse timestamp '2024-44-44'

Side-note: currently the issue seems to appear only for API/hammer side. In UI we do these checks, so the PAT won't be created unless it's valid per there checks as well.