Docker ci image/add dep and dependency checks jobs

What does this MR do?

Adds dep check (executed on each Pipeline) and dep status -old (to be executed with Pipeline Schedules) checks.

Why was this MR needed?

dep check will ensure that any changes in dependencies added during development are properly finalized (so Gopkg.toml, Gopkg.lock and vendor/* are consistent).

dep status, executed from time to time with Pipeline schedule, will let us know if there are an updates of used dependencies, available for the constraints specified in Gopkg.toml.

https://gitlab.com/gitlab-org/gitlab-runner/pipelines/32318340 shows an example of:

• a Pipeline that detects content of vendor/ not in sync with Gopkg.lock - https://gitlab.com/gitlab-org/gitlab-runner/-/jobs/105837983
• a Pipeline that contains dep status job (started with a specific env variable, that will be used for Pipeline Schedule) and that finds available updates with dep status - https://gitlab.com/gitlab-org/gitlab-runner/-/jobs/105837984

https://gitlab.com/gitlab-org/gitlab-runner/pipelines/32333735 shows an example of:

• a Pipeline that doesn't have dep status job (started from a normal push)
• a Pipeline that confirms that Gopkg.toml, Gopkg.lock and vendor/ are in sync - https://gitlab.com/gitlab-org/gitlab-runner/-/jobs/105895643

Are there points in the code the reviewer needs to double check?

Jobs were added to the Release stage, just like Static QA job, so we'll be able to test whole pipeline even if there will be some minor problems with dependencies. Maybe it's time to consider another stage introduced after Release that would hold such tests.

Does this MR meet the acceptance criteria?

• Documentation created/updated
• Added tests for this feature/bug
• In case of conflicts with master - branch was rebased

What are the relevant issue numbers?

#3450 (closed)

Follow up #3645