[DPE-2469] Add support for disabling the operator

[marceloneppel]

Issue

Bootstack needs a way to stop the charm events during a maintenance window.

Solution

Implemented the disable operation the same way as MySQL charms (canonical/mysql-k8s-operator#388 and canonical/mysql-operator#409).

[codecov]

Codecov Report

Attention: Patch coverage is 42.85714% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 80.96%. Comparing base (3b3e0f2) to head (ddf5e67).

Files	Patch %	Lines
src/charm.py	42.85%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #412      +/-   ##
==========================================
- Coverage   81.08%   80.96%   -0.12%     
==========================================
  Files          10       10              
  Lines        2252     2259       +7     
  Branches      362      363       +1     
==========================================
+ Hits         1826     1829       +3     
- Misses        351      354       +3     
- Partials       75       76       +1     

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