[WIP] feat: pressure reconciler

[yanksyoon]

Applicable spec:

Overview

• Adapts GitHub runner to work based on pressure reconciler from planner.

Rationale

• Updated design to rely on pressure for spawning machines rather than using reactive/non-reactive configuration.

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 for charmhub is updated.
• The PR is tagged with appropriate label (urgent, trivial, complex).
• The changelog is updated with changes that affects the users of the charm.
• The application version number is updated in github-runner-manager/pyproject.toml.

[cbartz]

continued the work in a new PR #732 to avoid having me in the "reviewer" role