Add Apache License 2.0

[rajpatta]

Summary

• Adds a top-level LICENSE file under the Apache License 2.0.
• The repository currently has no license, which means by default no usage rights are granted — this PR makes the terms explicit so downstream users can adopt the plugin with confidence.

Why Apache 2.0

• It's the standard license across the JVM/Gradle ecosystem (Gradle itself, the Android Gradle Plugin, and most published Gradle plugins).
• Includes an explicit patent grant, which protects both BrowserStack and downstream users from patent-related claims tied to contributions.
• Permissive and enterprise-friendly — customers can embed the plugin in proprietary build pipelines without copyleft concerns.

Notes

• Copyright line: Copyright 2018-2026 BrowserStack (year range based on first commit through current year).
• No source-file headers added in this PR — that can be a follow-up if desired. The LICENSE file alone is sufficient to establish project-wide licensing.

Test plan

• Confirm LICENSE renders correctly on the repo landing page and is detected by GitHub's license picker.
• Confirm the copyright holder string matches BrowserStack's preferred legal/brand convention (open to changing to BrowserStack Limited or similar if preferred).