Update Gradle to 8.7, AGP to 8.4.0

[0xnm]

What does this PR do?

This PR updates Gradle version to 8.7 and AGP to 8.4.0 in 2 different commits: one updates it for the build env, another one updates it for the functional tests run.

This PR also removes Detekt from the build script - it is run externally in the static-analysis nested pipeline and it was using old version 1.17.0, which doesn't work with the change made.

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 :white_check_mark:

Project coverage is 81.42%. Comparing base (5368d30) to head (284cc34).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #253 +/- ## ============================================= + Coverage 81.38% 81.42% +0.05% - Complexity 202 204 +2 ============================================= Files 26 26 Lines 800 802 +2 Branches 103 104 +1 ============================================= + Hits 651 653 +2 Misses 112 112 Partials 37 37 ``` [see 2 files with indirect coverage changes](https://app.codecov.io/gh/DataDog/dd-sdk-android-gradle-plugin/pull/253/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=DataDog)