Replace Magic Strings with literals.py Constants

[mateoflorido]

Overview

Replace magic string in the codebase with constants.

Rationale

To align with the best practices from other charms and improve the code maintainability, this pull request replaces the "magic strings" used in the code with constants.

[addyess]

Amazing work, also liked the drive by

[addyess]

wow yes king!

[louiseschmidtgen]

Great work, thanks Mateo!

[github-actions]

Test coverage for 8ef33d2

coverage-report: install_deps /home/runner/work/k8s-operator/k8s-operator/charms/worker/k8s> python -I -m pip install 'coverage[toml]'
coverage-report: commands[0] /home/runner/work/k8s-operator/k8s-operator/charms/worker/k8s> coverage report
Name                                    Stmts   Miss  Cover
-----------------------------------------------------------
lib/charms/k8s/v0/k8sd_api_manager.py     278     29    90%
src/charm.py                              489    242    51%
src/cloud_integration.py                   80      3    96%
src/config/extra_args.py                   27      1    96%
src/containerd.py                         140     16    89%
src/cos_integration.py                     33     12    64%
src/events/update_status.py                51     10    80%
src/inspector.py                           40      4    90%
src/kube_control.py                        39     31    21%
src/literals.py                            21      0   100%
src/protocols.py                           26      5    81%
src/reschedule.py                          77      4    95%
src/snap.py                               185     26    86%
src/token_distributor.py                  181    109    40%
src/upgrade.py                            105     48    54%
-----------------------------------------------------------
TOTAL                                    1772    540    70%
coverage-report: OK (1.23=setup[1.02]+cmd[0.21] seconds)
congratulations :) (1.28 seconds)

Static code analysis report

Run started:2024-12-05 13:51:48.382599

Test results:
  No issues identified.

Code scanned:
  Total lines of code: 3789
  Total lines skipped (#nosec): 3
  Total potential issues skipped due to specifically being disabled (e.g., #nosec BXXX): 0

Run metrics:
  Total issues (by severity):
  	Undefined: 0
  	Low: 0
  	Medium: 0
  	High: 0
  Total issues (by confidence):
  	Undefined: 0
  	Low: 0
  	Medium: 0
  	High: 0
Files skipped (0):