Dockerfile: Use upstream go-swagger

[vvoland]

• related to: Remove use of "go-swagger" fork, and update to current version #42593

- What I did
Replaced an outdated fork of go-swagger (based on some version from 2016) with a recent upstream version.
The recent version fixes the lack of omitempty for the x-nullable fields (see #47526 (comment)).

However, there's one catch...

Old version did have a --skip-validator switch which turned off generation of the Validate method for the generated models. It has been removed somewhere around 2018 and is no longer available in the recent version.

While not harmful, we don't make any use of these validators, so they're only bloating our api definitions and requiring more dependencies in our api package:

	"github.com/go-openapi/errors"
	"github.com/go-openapi/strfmt"
	"github.com/go-openapi/validate"

Restoring this option is pretty straightforward, as the generator backend already has an option for that.
See: vvoland/go-swagger@0448fe8

If we want to skip generating these, we should:

1. Make our own fork that restores this option (we already have https://github.com/moby/go-swagger?)
2. Check with the upstream if they would be willing to accept it

- How to verify it
CI

- Description for the changelog

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