Lock devcontainer postgres to version 17

[lunkwill42]

Scope and purpose

Using the "latest" tag runs the risk of spontaneous upgrades during environment restarts. The data directory is persistent, but newer versions of PostgreSQL cannot use the data directory of an older version without some specific intervention to upgrade the data directory.

It's best to keep the upgrade behavior predictable; this does it by locking to a specific PostgreSQL version.

Additionally, this ensures the main devcontainer is provisioned with PostgreSQL client programs that match the selected PostgreSQL server version, so that programs like pg_dump will work correctly.

Contributor Checklist

Every pull request should have this checklist filled out, no matter how small it is.
More information about contributing to NAV can be found in the
Hacker's guide to NAV.

• Added a changelog fragment for towncrier
• Added/amended tests for new/changed code
• Added/changed documentation
• Linted/formatted the code with ruff, easiest by using pre-commit
• Wrote the commit message so that the first line continues the sentence "If applied, this commit will ...", starts with a capital letter, does not end with punctuation and is 50 characters or less long. See https://cbea.ms/git-commit/
• Based this pull request on the correct upstream branch: For a patch/bugfix affecting the latest stable version, it should be based on that version's branch (<major>.<minor>.x). For a new feature or other additions, it should be based on master.
• If applicable: Created new issues if this PR does not fix the issue completely/there is further work to be done
• If it's not obvious from a linked issue, described how to interact with NAV in order for a reviewer to observe the effects of this change first-hand (commands, URLs, UI interactions)
• If this results in changes in the UI: Added screenshots of the before and after
• If this adds a new Python source code file: Added the boilerplate header to that file

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

Test results

    27 files      27 suites   45m 40s ⏱️
 2 665 tests  2 665 ✅ 0 💤 0 ❌
19 710 runs  19 710 ✅ 0 💤 0 ❌

Results for commit c6398aa.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 62.81%. Comparing base (16d6419) to head (c6398aa).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3649      +/-   ##
==========================================
- Coverage   62.82%   62.81%   -0.02%     
==========================================
  Files         611      611              
  Lines       45125    45125              
  Branches       43       43              
==========================================
- Hits        28351    28344       -7     
- Misses      16764    16771       +7     
  Partials       10       10              

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