fix anchor links on API page #19271

Description:

This is actually a very "dirty" fix for the problem.

I tried fixing this in javascript first. But that wasn't that easy and it will change again when being migrated to vue nevertheless. This topic might need to be revisited then maybe.

ping @diosmosis

fixes #19252

Review

• [ ] Functional review done
• [ ] Potential edge cases thought about (behavior of the code with strange input, with strange internal state or possible interactions with other Matomo subsystems)
• [ ] Usability review done (is anything maybe unclear or think about anything that would cause people to reach out to support)
• [ ] Security review done
• [ ] Wording review done
• [ ] Code review done
• [ ] Tests were added if useful/possible
• [ ] Reviewed for breaking changes
• [ ] Developer changelog updated if needed
• [ ] Documentation added if needed
• [ ] Existing documentation updated if needed