Update Apache License Copyright Headers to CNCF Format

[markmandel]

Agones is a CNCF project, and we need to update our source file copyright headers to follow the CNCF-recommended format. This ensures that the copyright is attributed to the project contributors under the Linux Foundation's umbrella.

As per the CNCF Copyright Notices guidelines, the copyright notice should be updated to:
Copyright Contributors to Agones a Series of LF Projects, LLC.

Tasks:

• Identify all source files containing old copyright notices (e.g., Copyright 2017 Google LLC).
• Update headers in Go files (*.go).
• Update headers in Protocol Buffer files (*.proto).
• Update headers in Shell scripts (*.sh).
• Update headers in YAML/Configuration files where applicable.
• Ensure the LICENSE file and any NOTICE files are consistent with this change.

Proposed Header Change:

Before:

// Copyright 2017 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
...

After:

// Copyright Contributors to Agones a Series of LF Projects, LLC.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
...

References:

• CNCF Foundation - Copyright Notices

[lacroixthomas]

Huge PR incoming with this one 😄

[markmandel]

Could also do this in chunks - doesn't have to be done in one go.

[mateenali66]

happy to take this on. saw the note about chunking, but one sweep across all file types (go/proto/sh/yaml) would avoid merge-conflict churn and keep the history clean. any objection to doing it in a single PR? if chunking is preferred I can start with *.go and follow up with the rest. could you assign it to me?

[markmandel]

Some done! Bit more to go!

[JeevaRamanathan]

I would like to work on vendor/ directory