Fix rolling restart by adding a dedicated callback method

[nrobinaubertin]

Overview

Add handler method for rolling restart to be used as callback method for the RollingOpsManager.

Checklist

• The charm style guide was applied
• The contributing guide was applied
• The changes are compliant with ISD054 - Manging 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 5f09a4d

Name              Stmts   Miss Branch BrPart  Cover   Missing
-------------------------------------------------------------
src/charm.py        330     30     82     11    90%   177, 185-186, 350->355, 548-550, 555-556, 567-569, 574-575, 587-589, 594-595, 607-609, 634-636, 676->exit, 686->exit, 716-722, 748->exit, 762-763, 773->exit, 787
src/database.py      30      1      8      1    95%   56
-------------------------------------------------------------
TOTAL               360     31     90     12    90%

Static code analysis report

Run started:2024-01-17 16:10:10.386452

Test results:
  No issues identified.

Code scanned:
  Total lines of code: 1984
  Total lines skipped (#nosec): 1
  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):