Use HomeFragment's viewLifecycleOwner as the lifecycle for observer registry

[grigoryk]

If we just use the HomeFragment itself, we end up with a memory leak since the lifecycle events
that would clean up the registry (e.g. destroy) won't run (if the fragment is retained in the backstack, for example).

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.

After merge

• Milestone: Make sure issues finished by this pull request are added to the milestone of the version currently in development.

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[codecov-io]

Codecov Report

Merging #10012 into master will decrease coverage by 0.00%.
The diff coverage is 0.00%.

@@             Coverage Diff              @@
##             master   #10012      +/-   ##
============================================
- Coverage     19.17%   19.16%   -0.01%     
  Complexity      521      521              
============================================
  Files           336      336              
  Lines         13729    13731       +2     
  Branches       1844     1844              
============================================
  Hits           2632     2632              
- Misses        10857    10859       +2     
  Partials        240      240              

Impacted Files	Coverage Δ	Complexity Δ
...c/main/java/org/mozilla/fenix/home/HomeFragment.kt	0.00% <0.00%> (ø)	0.00 <0.00> (ø)

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[ekager]

🤞🏻 hoping this fixes #9936 but either way happy to fix some memory leaks!