Certificate type handling improvements

This MR includes some improvements in code readability, documentation, and logging with regards to certificate type handling.

Checklist

• Commits have Signed-off-by: with name/author being identical to the commit author
• Code modified for feature
• Test suite updated with functionality tests
• Test suite updated with negative tests
• Documentation updated / NEWS entry present (for non-trivial changes)
• CI timeout is 2h or higher (see Settings/CICD/General pipelines/Timeout)

Reviewer's checklist:

• Any issues marked for closing are addressed
• There is a test suite reasonably covering new functionality or modifications
• Function naming, parameters, return values, types, etc., are consistent and according to CONTRIBUTION.md
• This feature/change has adequate documentation added
• No obvious mistakes in the code

marked the checklist item Commits have Signed-off-by: with name/author being identical to the commit author as completed

marked the checklist item CI timeout is 2h or higher (see Settings/CICD/General pipelines/Timeout) as completed

marked the checklist item Code modified for feature as completed

marked the checklist item Documentation updated / NEWS entry present (for non-trivial changes) as completed

marked the checklist item No obvious mistakes in the code as completed

added 5 commits

• 6f9d5613 - Added extra logging and done some variable refactoring for client cert type extension.
• 3a7ef798 - Added extra logging and done some variable refactoring for server cert type extension.
• d28825da - Added documentation for rawpk use in certificate retrieval callback.
• 4703ed1a - Changed certificate retrieval callback prototype parameter name to be in line...
• 374c84a0 - Changed _gnutls_session_cert_type_supported prototype and name to follow...

Compare with previous version

resolved all threads

marked the checklist item Any issues marked for closing are addressed as completed

approved this merge request

mentioned in commit 857543cc

merged

Thank you!