For #15537 - Be more verbose about leanplum identifiers

[st3fan]

This patch logs the usage of Leanplum identifiers so that it makes it easier to debug #15392 If we think this is low risk then I would like to uplift this patch to 8.1.2 as getting LP messaging working is a very high priority.

Pull Request checklist

• Tests: This PR includes thorough tests or an explanation of why it does not
• Screenshots: This PR includes screenshots or GIFs of the changes made or an explanation of why it does not
• Accessibility: The code in this PR follows accessibility best practices or does not include any user facing features. In addition, it includes a screenshot of a successful accessibility scan to ensure no new defects are added to the product.

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[codecov-commenter]

Codecov Report

Merging #15538 into master will increase coverage by 0.00%.
The diff coverage is 0.00%.

@@            Coverage Diff            @@
##             master   #15538   +/-   ##
=========================================
  Coverage     29.84%   29.84%           
- Complexity     1180     1182    +2     
=========================================
  Files           452      452           
  Lines         18387    18392    +5     
  Branches       2372     2373    +1     
=========================================
+ Hits           5488     5490    +2     
- Misses        12512    12516    +4     
+ Partials        387      386    -1     

Impacted Files	Coverage Δ	Complexity Δ
...fenix/components/metrics/LeanplumMetricsService.kt	23.84% <0.00%> (-0.96%)	3.00 <0.00> (ø)
...in/java/org/mozilla/fenix/settings/SupportUtils.kt	74.50% <0.00%> (+3.92%)	13.00% <0.00%> (+2.00%)

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