Launchpad itself

When I originally added code to change `RLIMIT_NOFILE` here, the intent
was to _raise_ the limit from the relatively low OS default. However,
since then, we've switched to running `buildd-manager` from a systemd
service deployed via a charm, and
`charm/launchpad-buildd-manager/templates/launchpad-buildd-manager.service.j2`
sets `LimitNOFILE=65536`; as a result, this code now has the effect of
_lowering_ the limit.

Let's just rely entirely on the configuration in the systemd service.

7cad6e3... by Colin Watson on 2023-09-05

Bump buildd-manager open file limit some more

Merged from https://code.launchpad.net/~cjwatson/launchpad/+git/launchpad/+merge/450646

6e57786... by Colin Watson on 2023-09-05

Bump buildd-manager open file limit some more

We're bumping into the current limit on production, and I think it's
because a few things have changed since we last set that limit: we have
more active builders, and we make a few more outgoing connections than
we did then (particularly to issue tokens for private builds). Make the
limit more generous.

0496488... by Simone Pelosi on 2023-09-04

Drop `value_type` to leave dict values unvalidated

Weakening `value_type` validation we can support `_byarch` member
in `auto_build_channels` variable. This should be converted later in
a custom validation for `_byarch`.

LP: #2033382

Merged from https://code.launchpad.net/~pelpsi/launchpad/+git/launchpad/+merge/450364

ded226a... by Colin Watson on 2023-09-04