acceptance: run python, psql containers as current uid

[rickystewart]

postgres's permission checking for certificates has gotten more
rigorous since this commit.
This has broken a couple acceptance tests which do not pin to any
specific postgres version (see #81313, #81437).

Here we attempt to solve the problem "once and for all" by ensuring that
these containers run with a UID that is equal to the one that created
the certificates.

Release note: None

[cockroach-teamcity]

This change is 

[rickystewart]

@knz -- Looks like TestComposeGSS has some problems with this:

psql_1       | psql: local user with ID 1006 does not exist

Not sure what changes are necessary at this point.

[knz]

it's amissing entry in /etc/passwd.
need to add https://github.com/benesch/autouseradd like in builder image.

[knz]

awesome, thanks

Reviewed 6 of 6 files at r1, all commit messages.
Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @rickystewart)

[rickystewart]

TFTR!

bors r=knz

[otan]

i assume we're backporting these, so i'm adding the tags!

[craig]

This PR was included in a batch that was canceled, it will be automatically retried

[craig]

Build succeeded:

• GitHub CI (Cockroach)

[blathers-crl]

Encountered an error creating backports. Some common things that can go wrong:

1. The backport branch might have already existed.
2. There was a merge conflict.
3. The backport branch contained merge commits.

You might need to create your backport manually using the backport tool.

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error creating merge commit from 3ef77d5 to blathers/backport-release-21.2-81460: POST https://api.github.com/repos/cockroachdb/cockroach/merges: 409 Merge conflict []

you may need to manually resolve merge conflicts with the backport tool.

Backport to branch 21.2.x failed. See errors above.

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