Allow pipeline schedule owner to call take_ownership API

What does this MR do and why?

Describe in detail what your merge request does and why.

Currently, a user is granted the take_ownership_pipeline_schedule ability if they have the admin_pipeline_schedule ability and are not already the owner of the schedule. This results in the take_ownership API returning 403 if the user calling the API is already the owner of the schedule, which can be confusing.

This MR removes the take_ownership_pipeline_schedule ability and instead allows users with the admin_pipeline_schedule ability to take ownership of the schedule.

This allows the API to succeed even if the user is already the owner of the pipeline schedule.

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.