Use repo-file-sync-action to standardise pre-commit-config.yaml

[trexfeathers]

You can see a demo of this working here: trexfeathers/iris#88 (I tweaked certain config to temporarily make this work locally).

Don't bother looking at the commit sequence - lots of trial and error. Just look at the diff 😅

Further explanation:

.github/templates/README.md

Lines 1 to 19 in 33d12ba

	These files are templates defining the standard format across all SciTools
	repos. Repo deviations from template are periodically identified in pull
	requests by the repo-file-sync-action.
	### Possible actions on a deviation pull request
	- ✔️ **Merge** - all deviations are re-aligned with the template
	(E.g. the repo is simply out of date and needs updating).
	- ❌ **Close** - all deviations are kept
	(E.g. all deviations are required repo-specific detail).
	- ️️✏️ **Edit** - re-align some deviations, keep others.
	- 🏃 **Close then action independently**
	(E.g. the repo contains content that should be added to the template).
	### Further reading
	- https://github.com/marketplace/actions/repo-file-sync-action
	- [../.github/workflows/template-sync.yml](../.github/workflows/template-sync.yml)
	- [../.github/template-sync.yml](../.github/template-sync.yml)

[HGWright]

Looks great, thanks for this new GHA! @trexfeathers