[Docs] Make it possible to regenerate older docs with additional patch(es)

[asfimport]

We may need to regenerate older docs to include new changes, e.g. the new version dropdown feature.

Since we need to regenerate the docs for the first time, it would be great if we could encapsulate this in a script. After applying the patch archery docker run ubuntu-docs should do the rest, similarly like we use in the post-release task https://github.com/apache/arrow/blob/master/dev/release/post-09-docs.sh

dev/release/generate-docs.sh <version> <patch>

dev/release/generate-docs.sh 6.0.0  # no patch required
dev/release/generate-docs.sh 5.0.0 docs.patch
dev/release/generate-docs.sh 4.0.0 docs.patch
dev/release/generate-docs.sh 3.0.0 docs.patch

1. then deploy to asf-site

cc @jorisvandenbossche

Reporter: Krisztian Szucs / @kszucs

_{Note: This issue was originally created as ARROW-14498. Please see the migration documentation for further details.}

[asfimport]

Joris Van den Bossche / @jorisvandenbossche:
Personally, I don't think we need to do this 1) for all versions, and 2) make this a habit.

It's only now when introducing the versioned docs it's useful to regenerate some older versions (I was personally thinking to only do it for 5.0, and we don't even have to do it at all).

Also, for older versions, it's not a given that the current theme will work nicely with older sphinx versions. And more importantly, those patches probably won't apply cleanly to those older docs since many other things have changed in the meantime (eg the older docs before 4.0 actually use a different sphinx theme, so practically speaking it's only 4.0 and 5.0 that could be regenerated).

(that doesn't mean we can't keep good track of how we did it now once for 5.0, so if it turns out we will do this regularly later, it's easy to convert that into a script)