Set lower limits for create/update/delete of postgres gateway users

[einarmo]

Description

Set the limit for number of postgres gateway users to create/update/delete to 1.

These operations have a tendency to be extremely heavy, so the limits are low for now.

Checklist:

• Tests added/updated.
• Documentation updated. Documentation is generated from docstrings - these must be updated according to your change.
  If a new method has been added it should be referenced in cognite.rst in order to generate docs based on its docstring.
• Changelog updated in CHANGELOG.md.
• Version bumped. If triggering a new release is desired, bump the version number in _version.py and pyproject.toml per semantic versioning.

[haakonvt]

LGTM

[haakonvt]

Unrelated tests fail currently due to #2102 , I'll see if I can get that fixed by EOD. Set it to auto-merge if you want, and I'll see it through.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.69%. Comparing base (28faa0c) to head (4d7591e).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2105   +/-   ##
=======================================
  Coverage   90.68%   90.69%           
=======================================
  Files         149      149           
  Lines       22881    22886    +5     
=======================================
+ Hits        20750    20756    +6     
+ Misses       2131     2130    -1     

Files with missing lines	Coverage Δ
cognite/client/_api/postgres_gateway/users.py	94.64% <100.00%> (+0.52%)	⬆️

... and 3 files with indirect coverage changes