Update RELEASE.md to use gh release

[CharlieTLe]

The RELEASE.md instructions should use gh release to manage the release.

For example, instead of going to the UI to upload the artifacts, we could do something like

$ gh release -R github.com/cortexproject/cortex upload v1.19.0-rc.1 sbom.tar.gz sbom.tar.gz.asc
Successfully uploaded 2 assets to v1.19.0-rc.1

to upload the artifacts programmatically.

More info: https://cli.github.com/manual/

[stale]

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