(WIP) Test missing logging call linter

[marceloneppel]

Issue

We usually forget to add logging calls at the early exits of the charm code.

Solution

Add a linter to catch missing logging calls and report them as a warning (maybe block a PR from being merged in the future)

How to test this PR:

# Set up Vex. You need Rust for it: curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
git clone https://github.com/TheSignPainter98/vex
cd vex/
cargo install --path .

# Check out this PR.
cd ..
git clone https://github.com/canonical/postgresql-k8s-operator
cd postgresql-k8s-operator
git checkout test-missing-logging-call-linter

# Check for the missing logging calls.
vex check

Sample output:

warning[logging]: return statement without logging call
   --> src/relations/async_replication.py:526:9
    |
526 |           if self._wait_for_standby_leader(event):
    |  _________-
527 | |             return
    | |__________________- consider adding the logging call
    |
warning: found 1 problem

TODO:

• Check the elif and else clauses.
• Ignore cases where a call to another function already did some logging call on that function.
• Add vex check to the CI workflow.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.56%. Comparing base (293b597) to head (c4c869f).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #764      +/-   ##
==========================================
- Coverage   75.65%   75.56%   -0.10%     
==========================================
  Files          12       12              
  Lines        3110     3110              
  Branches      474      474              
==========================================
- Hits         2353     2350       -3     
- Misses        614      617       +3     
  Partials      143      143              

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