Draft: On-call schedule timeline sandbox

THIS MERGE WILL NEVER BE MERGED

What does this MR do?

Shared sandbox for pairing sessions between @oregand and @tristan.read.

This merge as a Draft represents a DoD for reference as we aim to break the work in this merge into 5 smaller merges and this can be used as a reference for the overall goal. At the end of our 5 merges, we should see a significant decrease in code volume for On-call schedules.

What	Merge
Introduce new helper for shift utils	!58202 (merged)
Update shift width query	!58204 (merged)
Consolidate Week and Day shift items	!58322 (merged)
Render grid as single timeline cell and update day indicator	!58342 (merged)
Remove old code	!58352 (merged)
Add integration specs	TBA
Replace inline JS with CSS media queries for rotation assignee	TBA

Screenshots (strongly suggested)

before	after

Does this MR meet the acceptance criteria?

Conformity

This merge will never be merged

Related to #324608 (closed)