Add testing docs.

[terabytesoftw]

Q	A
Is bugfix?	❌
New feature?	✔️
Breaks BC?	❌

[what-the-diff]

PR Summary

• Added Docker support for MySQL and MariaDB
  Docker-compose files for MySQL and MariaDB have been added to ease setup and use.
• Updated README with relevant testing information
  The README file has been updated with important testing information, and old irrelevant content has been removed.
• New documentation page for testing
  A new documentation page has been created to provide detailed information about testing the package (located in docs/en/testing).

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (08a0973) 99.11% compared to head (a5f7703) 99.11%.

❗ Current head a5f7703 differs from pull request most recent head 9597c96. Consider uploading reports for the commit 9597c96 to get more accurate results

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #269   +/-   ##
=========================================
  Coverage     99.11%   99.11%           
  Complexity      191      191           
=========================================
  Files            13       13           
  Lines           566      566           
=========================================
  Hits            561      561           
  Misses            5        5           

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