Compare our use of scanspec with that from core

In https://github.com/DiamondLightSource/dodal/pull/793/files @DiamondJoseph added the `spec_scan` plan. We also have plans that make use of scanspec and should check if there's overlap. If nothing else we could standardise on some metadata names e.g. Their plan uses `shape` where we use `scan_points`.

## Acceptance Criteria
- Notes are written on here comparing `spec_scan` with how we use scanspec
- This might make sense to be done in discussion with core
- If there is commonality the two plans are made more common