Add backup and restore and external access documentation

[javierdelapuente]

Overview

Add documentation for the backup and restore procedure (redeployment) and also for the external accesses needed by the Discourse charm.

Rationale

Juju Events Changes

Module Changes

Library Changes

Checklist

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

[github-actions[bot]]

Test coverage for f41e5ea37e7da421496c9cc847e708bfe125938f

Name              Stmts   Miss Branch BrPart  Cover   Missing
-------------------------------------------------------------
src/charm.py        321     27     78     12    90%   186, 194-195, 207, 335->343, 376->381, 393, 581-583, 588-589, 601-603, 608-609, 621-623, 646-648, 690->exit, 700->exit, 730-736, 762->exit, 776-777, 787->exit, 801
src/database.py      30      1      8      1    95%   56
-------------------------------------------------------------
TOTAL               351     28     86     13    91%

Static code analysis report

Run started:2024-04-30 11:08:06.354915

Test results:
    No issues identified.

Code scanned:
    Total lines of code: 1984
    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):