Docker app build

[ndeloof]

- What I did Introduce support for "build" in docker app relying on buildx

- How I did it Mostly by vendoring buildx bake command. bundle command has been removed as obsolete push command has been updated

- How to verify it includes a dedicated e2e test

- Description for the changelog Introduce docker app build command

- A picture of a cute animal (not mandatory but encouraged)

[codecov[bot]]

Codecov Report

Merging #655 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #655   +/-   ##
=======================================
  Coverage   71.21%   71.21%           
=======================================
  Files          57       57           
  Lines        3088     3088           
=======================================
  Hits         2199     2199           
  Misses        599      599           
  Partials      290      290

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[GordonTheTurtle]

Please sign your commits following these rules: https://github.com/moby/moby/blob/master/CONTRIBUTING.md#sign-your-work The easiest way to do this is to amend the last commit:

$ git clone -b "build" git@github.com:ndeloof/app.git somewhere
$ cd somewhere
$ git rebase -i HEAD~842353997936
editor opens
change each 'pick' to 'edit'
save the file and quit
$ git commit --amend -s --no-edit
$ git rebase --continue # and repeat the amend for each commit
$ git push -f

Amending updates the existing PR. You DO NOT need to open a new one.