Changed .wharf-ci.yml for canary builds

[applejag]

• I've added a new note in the CHANGELOG.md file, according to docs:
  https://iver-wharf.github.io/#/development/changelogs/writing-changelogs

Summary

• Changed deploy tag in .wharf-ci.yml to :canary
• Changed to use our internal Docker Hub registry caching proxy in Docker builds
• Fixed Wharf build step name in .wharf-ci.yml

Motivation

Minor tweaks to make the Wharf builds work and be able to build Wharf itself.

The image tag name :unstable is up for debate. Perhaps :canary? Or simply :latest? Changed to :canary.

Related to iver-wharf/iver-wharf.github.io#80

This is the first PR I'm marking "Ready for review". Let's have all discussions in this PR to begin with, as the other PRs listed in the meta-issue above are basically just the same.

[fredx30]

Whats the use case for this?
Edit: Nvm i think it might be the continuation to the discussion over the earlier named "development" environment. I still think this would be better off tied to a specific branch rather than just tags.

Also the name unstable just seems like code for undesierable. I would preffer canary to unstable if those are the available choices.

Also i think lastest should be only prod build such that the tag moves with the actualy releases.

[applejag]

@fredx30 /.../ I still think this would be better off tied to a specific branch rather than just tags.

The planned flow is as follows:

1. Go to our internal wharf-web instance

2. Find project iver-wharf/wharf-api

3. Press start new build

4. Select branch you want deployed
   

5. Once build has finished, find our "deploy-unstable"/"deploy-canary" project and start a new build there

6. Done

This depends on branches and not on just tags. Or are you referring to the Docker image tag?

[Alexamakans]

LGTM 👍🏻