Follow-up: Generate the branches list for status checks form once and save in the store

The following discussion from !61700 (merged) should be addressed:

• @rob.hunt started a discussion:

  Note: This is currently run for every branch. Since we can have multiple of these, it would be more performant and better memory usage for us to get this value initially and then store it in the status checks store. We can then re-use the same initial branches for all branch select components