[admin] Consider committing the built tailwind css file into the admin repo

[elia]

          What do you think about committing the built tailwind css file into the admin repo (and update it on PR merge)? That file won't change much (at least once the admin has been built out). And even until then it makes sense to have it updated regularly (not just on gem release).

People might use solidus_admin from git source like this

# Gemfile
gem "solidus_admin", github: "solidusio/solidus", branch: "v4.3"

(in order to get bug fixes early for stable versions that have not been released yet.)

We want to make sure they get the admin css file, right?

Originally posted by @tvdeyen in #5595 (comment)

[tvdeyen]

With the recent issues on CircleCI regarding the tailwind rake task we install in all host apps (!!) I think we really should do that. We are doing this for a very long time in Alchemy and we have zero issues or complaints.