chores: add nginx to maubot

[amandahla]

Applicable spec:

Overview

Move NGINX to Maubot as suggested in #9 by @weiiwang01

Also remove handling exception raised by Pebble, leaving them to raise as Juju errors. The charm handle only exceptions if the user can take action. Catched it here by @Thanhphan1147

Rationale

Use only one container for Maubot.

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)

[github-actions]

Test coverage for e9cd8dd

Name           Stmts   Miss Branch BrPart  Cover   Missing
----------------------------------------------------------
src/charm.py      70      4      8      1    94%   101, 105, 114, 136
----------------------------------------------------------
TOTAL             70      4      8      1    94%

Static code analysis report

Run started:2024-09-23 14:12:02.369560

Test results:
  No issues identified.

Code scanned:
  Total lines of code: 288
  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):