Support a charm resource to override the installed snap

[addyess]

Overview

Create support to override the snap, while warning users they are using the charm in an override mode

Rationale

In order to test that new builds of the k8s snap will operate on the current stable k8s charm, we should be able to verify the snap before releasing it. To do so, we need a way to insert the snap into the charmed environment. This provides the ability to do so.

[mateoflorido]

LGTM!

[github-actions]

Test coverage for e317fe3

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     270     29    89%
src/charm.py                              461    247    46%
src/cloud_integration.py                   80      3    96%
src/containerd.py                         140     16    89%
src/cos_integration.py                     33     12    64%
src/events/update_status.py                48     10    79%
src/inspector.py                           40      3    92%
src/kube_control.py                        39     31    21%
src/literals.py                             1      0   100%
src/protocols.py                           16      3    81%
src/reschedule.py                          77      4    95%
src/snap.py                               165     10    94%
src/token_distributor.py                  174    103    41%
src/upgrade.py                             31      1    97%
-----------------------------------------------------------
TOTAL                                    1575    472    70%
coverage-report: OK (1.19=setup[0.99]+cmd[0.20] seconds)
congratulations :) (1.24 seconds)

Static code analysis report

Run started:2024-11-21 15:44:16.467696

Test results:
  No issues identified.

Code scanned:
  Total lines of code: 3380
  Total lines skipped (#nosec): 13
  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):