Remove `help_text` from reader-study serialization

[pkcakeout]

The name help_text is going to be retired because it was replaced by help_text_safe in the reader-study API. We need to wait fro two CIRRUS release to until we can remove this safely. After the October 2025-cycle, we can remove it.

[jmsmkn]

There are more fields than just help text, see the linked PR.

Also requires an update to GCAPI models.

[chrisvanrun]

And a direct release of GCAPI to account for the changes.