Allow to give services an alias

What does this MR do?

Allow docker services referenced in .gitlab-ci.yml to be aliased.

Example:

services:
  - kaixhin/ssh as origin
  - kaixhin/ssh as destination

The as part is optional, should be backwards compatible.

Why was this MR needed?

• The generated names aren't always intuitive and can become very long.
• A service can only be used once, which is limiting (e.g. we needed to transfer files between two ssh hosts).

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

I have not worked with go before, so yes ;)

Does this MR meet the acceptance criteria?

• [ x] CHANGELOG entry added
• [ x] Documentation created/updated
• Tests
  • [ x] Added for this feature/bug
  • All builds are passing
• [ x] Branch has no merge conflicts with master (if you do - rebase it please)

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/issues/1284

I'm not sure it's the best way to do this, but I wanted to be downwards compatible. https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/issues/1284# suggests to use a map. This would also allow more elaborate configuration (and basically rebuild the structure docker-compose?)

Marked the task All builds are passing as completed

Marked the task All builds are passing as incomplete

Marked the task All builds are passing as completed

It's possible to be downwards compatible by allowing the two syntaxes: string (without as) and mapping object. Allow multiple syntaxes is actually quite common and, I think, more elegant than defining a weird syntax. That said, thank you to take care of it because it's a very important feature.

Thanks for the feedback! I absolutely agree, it's a bit hackish. If I find time I'll gladly look at an alternative implementation. As I said I think copying docker-compose would be the best solution. We'd not only solve the naming issue, but also a per-service configuration (i.e. per-service environment variables, volumes etc.). Any thoughts?

Any comments from the devs regarding this one?

Mentioned in issue #1284 (closed)

Any updates on this? This would be really useful functionality.

What is the progress of this MR right now?

I seem it looks good

Any update for this MR?