Add no-op experiment to test service-experiments integration

[mythmon]

This is for bug 1556751 This change helps verify that the service-experiments library is correctly integrated into Fenix, and that it can correctly enroll users in an experiment. This is exactly the same test that was done in mozilla-mobile/reference-browser#827. That reference browser population was not large enough to completely verify the library's behavior, but no red flags were raised.

I don't think this feature needs tests because it is itself a test of the experiments system.

I'm not sure if this change builds or not. I am having some trouble with the metrics metadata. I'm still working on this.

Pull Request checklist

• Quality: This PR builds and passes detekt/ktlint checks (A pre-push hook is recommended)
• Tests: This PR includes thorough tests or an explanation of why it does not
• Changelog: This PR includes a changelog entry or does not need one
• Accessibility: The code in this PR follows accessibility best practices or does not include any user facing features

[travis79]

LGTM, pending data review!

[boek]

🤦‍♂️ Great catch!

[mythmon]

Data review has passed, and I've updated this with the correct URL for it. I also rebased this PR atop master to fix a merge conflict.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@0c8bcd3). Click here to learn what that means.
The diff coverage is 0%.

@@           Coverage Diff            @@
##             master   #4551   +/-   ##
========================================
  Coverage          ?   6.73%           
  Complexity        ?     152           
========================================
  Files             ?     203           
  Lines             ?    8453           
  Branches          ?    1185           
========================================
  Hits              ?     569           
  Misses            ?    7845           
  Partials          ?      39

Impacted Files	Coverage Δ	Complexity Δ
...rc/main/java/org/mozilla/fenix/FenixApplication.kt	4.16% <0%> (ø)	2 <0> (?)

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[mythmon]

@travis79 can you take a look at this? I think it is ready to merge.

[travis79]

Data review has passed, and I've updated this with the correct URL for it. I also rebased this PR atop master to fix a merge conflict.

This looks good to me, my r+ still stands. Because I'm not a codeowner in this repo, we will still need someone with the correct permissions, such as @boek or @colintheshots to review as well.

[travis79]

I just asked about this in the Fenix-team channel on slack to see if we can get a reviewer for this (or if there is a process we need to follow to get on the radar for reviews)

[colintheshots]

This looks good. Thanks.