WIP/DNM feat: add public-url config

[amandahla]

Applicable spec:

Overview

This PR is not ready to review yet, I'm waiting for the #10

Adds public-url configuration.

"The public URL where the resources are available. The base path is automatically appended to this."
Extracted from the example config.

Rationale

Allow the user to change the public URL if needed.

Juju Events Changes

Module Changes

Library Changes

Checklist

• The charm style guide was applied
• The contributing guide was applied
• The changes are compliant with ISD054 - Managing Charm Complexity
• The documentation is generated using src-docs
• The documentation for charmhub is updated
• The PR is tagged with appropriate label (urgent, trivial, complex)

No CH available yet.

[github-actions]

Test coverage for a460509

Name           Stmts   Miss Branch BrPart  Cover   Missing
----------------------------------------------------------
src/charm.py      71      4      8      1    94%   102, 106, 115, 137
----------------------------------------------------------
TOTAL             71      4      8      1    94%

Static code analysis report

Run started:2024-09-23 19:46:51.979079

Test results:
  No issues identified.

Code scanned:
  Total lines of code: 308
  Total lines skipped (#nosec): 0
  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):