feat: Support to configure mariadb variables from dashboard

[tanmoysrt]

Fixes #2330

[codecov]

Codecov Report

Attention: Patch coverage is 43.33333% with 17 lines in your changes missing coverage. Please review.

Project coverage is 38.54%. Comparing base (7100f48) to head (e0b6198).

Files with missing lines	Patch %	Lines
...press/doctype/mariadb_variable/mariadb_variable.py	42.10%	11 Missing ⚠️
...s/press/doctype/database_server/database_server.py	45.45%	6 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2335   +/-   ##
=======================================
  Coverage   38.54%   38.54%           
=======================================
  Files         377      377           
  Lines       29237    29266   +29     
=======================================
+ Hits        11270    11282   +12     
- Misses      17967    17984   +17     

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