Port notice generator to Golang

[kvch]

Currently, the NOTICE.txt file is generated using the Python script dev-tools/generate_notice.py. To integrate better with mage and to utilize Golang specific tools, we should port the script to Golang.

[jsoriano]

When implementing this we have to take into account that dev-tools/generate_notice.py --csv is used by internal release processes.

[kvch]

We should evaluate if we can use this tool instead of creating our own: https://github.com/elastic/cloud-on-k8s/tree/master/hack/licence-detector

[botelastic]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[kvch]

Closing as have already adopted https://github.com/elastic/go-licence-detector in #18655