Properly quote descriptions in ad metric definitions

[wlach]

This is pedantic, but strictly something called <provider-name> is considered an HTML tag
unless it's in a code block (backticks). This can cause problems with downstream consumers like the glean dictionary unless we work around it there:

See mozilla/glean-dictionary#549 and mozilla/glean-dictionary#497. I'm working around this downstream in the glean dictionary now (I suspect this is going to crop up again and don't want to go around fixing this everywhere) but figured I might as well file a PR here while I was at it.

FWIW you can view this metric here: https://dictionary.protosaur.dev/apps/fenix/metrics/browser_search_ad_clicks

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 #19243 (68472a7) into master (eec6411) will decrease coverage by 0.00%.
The diff coverage is 41.30%.

@@             Coverage Diff              @@
##             master   #19243      +/-   ##
============================================
- Coverage     34.84%   34.84%   -0.01%     
+ Complexity     1653     1652       -1     
============================================
  Files           543      543              
  Lines         22006    22031      +25     
  Branches       3295     3301       +6     
============================================
+ Hits           7669     7677       +8     
- Misses        13430    13445      +15     
- Partials        907      909       +2     

Impacted Files	Coverage Δ	Complexity Δ
...org/mozilla/fenix/components/BackgroundServices.kt	20.83% <ø> (ø)	0.00 <0.00> (ø)
.../mozilla/fenix/search/awesomebar/AwesomeBarView.kt	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
...x/settings/creditcards/CreditCardEditorFragment.kt	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
...editcards/controller/CreditCardEditorController.kt	33.33% <ø> (ø)	0.00 <0.00> (ø)
...editcards/interactor/CreditCardEditorInteractor.kt	100.00% <ø> (ø)	0.00 <0.00> (ø)
.../settings/creditcards/view/CreditCardEditorView.kt	95.91% <88.23%> (-4.09%)	8.00 <0.00> (ø)
...src/main/java/org/mozilla/fenix/components/Core.kt	21.08% <100.00%> (+0.47%)	3.00 <0.00> (-1.00)	⬆️
...enix/settings/creditcards/CreditCardEditorState.kt	100.00% <100.00%> (ø)	7.00 <0.00> (ø)
...tings/creditcards/view/CreditCardItemViewHolder.kt	100.00% <100.00%> (ø)	3.00 <1.00> (ø)

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