Improve CI pipeline and image maintenance - #619

Summary

• Replaces the shared static-analysis pipeline with repository-owned Detekt, Ktlint, Android Lint, license, and generated-file checks aligned with dd-sdk-android.
• Centralizes Ktlint configuration, standardizes source headers, and converts the remaining Groovy build script to Kotlin DSL.
• Replaces JaCoCo and its flaky per-module coverage threshold with Kover 0.9.8 while preserving module-level Datadog coverage uploads.
• Streamlines the CI image and build context, embeds the checksum-verified Java tracer, updates Android tooling, and supports architecture-aware Datadog CI installation.
• Aligns pipeline stage naming and auto-cancels superseded short-lived branch pipelines while protecting stateful jobs.

Validation

• ./gradlew koverXmlReport :build-config:test :dd-sdk-android-gradle-plugin:checkThirdPartyLicences
• ./gradlew ktlintCheck :build-config:ktlintCheck detekt --continue
• ./gradlew checkGeneratedFiles --no-configuration-cache
• ./gradlew lintRelease --continue
• ./gradlew :samples:variants:tasks
• GitLab YAML and diff formatting checks

Notes

• These are CI and build-tooling changes; no plugin version bump is required.
• The manual ci-image job must publish and sign image 19.
• The full image build was not run locally because Docker was unavailable.