Add testing docs.

[terabytesoftw]

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

[what-the-diff]

PR Summary

• Added docker-compose file for Oracle 21
  Introduces a new configuration file for Oracle 21 support.
• Updated README with testing information
  Provides updated testing instructions and a link to the new documentation page.
• Added English documentation for testing
  A new document specifically for testing guidelines is now available in English.

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (14417c3) 98.15% compared to head (323da67) 98.15%.

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #201   +/-   ##
=========================================
  Coverage     98.15%   98.15%           
  Complexity      193      193           
=========================================
  Files            16       16           
  Lines           597      597           
=========================================
  Hits            586      586           
  Misses           11       11           

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

☔ View full report in Codecov by Sentry.
📢 Do you have feedback about the report comment? Let us know in this issue.