build: move tools/dev dependencies to a separate go.mod

What does this MR do?

Move tools/dev dependencies to a separate go.mod to slim down dependencies and have more accurate dependency scanning.

This is done in a way that is transparent to the user so they can just run make setup as usual. The only difference is that people using the gitlab-pages module won't have to depend on our dev/tools dependencies.

Note: tools.go.mod is using a different go.sum (tools.go.sum) so there are no conflicts

TODO

• I added the Changelog trailer (e.g. Changelog: feature) to the commits that need to be included in the changelog
• I added unit tests or they are not required
• I added acceptance tests or they are not required
• I added documentation (or it's not required)
• I followed code review guidelines
• I followed Go Style guidelines