Fix caching of models generation task

[0xnm]

What does this PR do?

This change fixes the caching of GenerateJsonSchemaTask task. Before it was reading input files by calling listFiles for the given input dir, which will return only top-level files.

But it can be the case that top-level files are actually only the reference to the files deeper, like this:

{
  "$schema": "http://json-schema.org/draft-07/schema",
  "$id": "session-replay-mobile-schema.json",
  "$ref": "session-replay/mobile/segment-schema.json"
}

It means that top-level file will receive no change when referenced file session-replay/mobile/segment-schema.json actually changes, making Gradle think that inputs didn't change and skipping models generation.

With this change we track all files recursively with Gradle, but take only top-level files for the model generation.

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)

[mariusc83]

I guess it can work...we are forcing it to only the root files

[codecov-commenter]

Codecov Report

Merging #1111 (3cb9b2f) into feature/sdkv2 (e201ff4) will decrease coverage by 0.17%.
The diff coverage is 92.39%.

@@                Coverage Diff                @@
##           feature/sdkv2    #1111      +/-   ##
=================================================
- Coverage          82.64%   82.47%   -0.17%     
=================================================
  Files                350      352       +2     
  Lines              11301    11415     +114     
  Branches            1846     1896      +50     
=================================================
+ Hits                9339     9414      +75     
- Misses              1396     1437      +41     
+ Partials             566      564       -2     

Impacted Files	Coverage Δ
...n/com/datadog/android/core/internal/CoreFeature.kt	91.09% <ø> (-0.35%)	⬇️
...in/com/datadog/android/core/internal/SdkFeature.kt	88.18% <ø> (ø)
...atadog/android/log/internal/domain/LogGenerator.kt	80.00% <ø> (-3.33%)	⬇️
...og/android/v2/core/internal/NoOpContextProvider.kt	3.57% <0.00%> (-0.78%)	⬇️
...play/internal/storage/SessionReplayRecordWriter.kt	16.67% <16.67%> (ø)
.../android/v2/log/internal/storage/LogsDataWriter.kt	60.00% <60.00%> (ø)
...g/android/sessionreplay/processor/NodeFlattener.kt	93.33% <83.33%> (+2.03%)	⬆️
.../android/error/internal/DatadogExceptionHandler.kt	81.08% <84.62%> (-4.63%)	⬇️
...atadog/android/sessionreplay/recorder/ViewUtils.kt	84.62% <84.62%> (ø)
...g/android/log/internal/logger/DatadogLogHandler.kt	90.91% <86.96%> (-0.76%)	⬇️
... and 45 more