Include Prometheus exporter into ROCK

[gtrkiller]

Applicable spec:

Overview

Install the statsd Prometheus exporter into gunicorn's ROCK

Rationale

This change simplifies the architecture of the charm by reducing the amount of resources and containers it needs

Juju Events Changes

N/A

Module Changes

N/A

Library Changes

N/A

Checklist

• [X] The charm style guide was applied
• [X] The contributing guide was applied
• [X] The changes are compliant with ISD054 - Managing 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 5cea130d1b403c6354bce7929471152f1445ca75

Name           Stmts   Miss Branch BrPart  Cover   Missing
----------------------------------------------------------
src/charm.py     188      0     68      1    99%   302->305
----------------------------------------------------------
TOTAL            188      0     68      1    99%

Static code analysis report

Run started:2024-01-18 14:11:30.182043

Test results:
    No issues identified.

Code scanned:
    Total lines of code: 1083
    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):