Pdok 18978/fix duplicate tags

[Dirc]

Description

• fix: handling of duplicate and empty tags: to fix errors when creating betterstack monitors
• fix: correct formatting in error message for response body. Log in string, not in bytes: for clear logs messages

Type of change

• Bugfix

Checklist:

• I've double-checked the code in this PR myself
• I've left the code better than before (boy scout rule)
• The code is readable, comments are added that explain hard or non-obvious parts.
• I've expanded/improved the (unit) tests, when applicable
• I've run (unit) tests that prove my solution works
• There's no sensitive information like credentials in my PR