Update LICENSE (#9)

The change replaces the short copyright boilerplate (which only pointed to the Apache 2.0 URL) with the full Apache License 2.0 text, and removes the two Copyright notices from LICENSE entirely. These are now in NOTICE.

NOTICE contains three copyright attribution lines:

  - Copyright 2019 Splunk, Inc. — the original authors
  - Copyright 2023 Cloudnatively Services, Pvt Ltd — subsequent maintainers
  - Copyright 2025 The Apache Software Foundation — the current ASF stewardship