Prevent obfuscation of Fine Grained Masking enums

[jonathanmos]

What does this PR do?

Adds a proguard rule to prevent the fine grained masking enums from being obfuscated.

Motivation

Because we resolve String --> Enum with valueOf.

Additional Notes

Anything else we should know when reviewing?

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• Make sure you discussed the feature or bugfix with the maintaining team in an Issue
• Make sure each commit and the PR mention the Issue number (cf the CONTRIBUTING doc)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.34%. Comparing base (ca952c5) to head (2d03936).
Report is 2 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2321      +/-   ##
===========================================
- Coverage    70.37%   70.34%   -0.03%     
===========================================
  Files          738      738              
  Lines        27529    27532       +3     
  Branches      4616     4616              
===========================================
- Hits         19372    19367       -5     
- Misses        6864     6874      +10     
+ Partials      1293     1291       -2     

Files with missing lines	Coverage Δ
.../com/datadog/android/sessionreplay/ImagePrivacy.kt	100.00% <ø> (ø)
...tadog/android/sessionreplay/TextAndInputPrivacy.kt	100.00% <ø> (ø)
.../com/datadog/android/sessionreplay/TouchPrivacy.kt	100.00% <ø> (ø)

... and 37 files with indirect coverage changes