Add GitHub action to publish docker reproducible builds

[jimmygchen]

Now that we have a reproducible Docker build implemented in #6799, we’d like to extend the release workflow to:

• Build the Docker images as part of the release workflow
• Publish the images to DockerHub

This should replace the current Docker image builds, which aren't built via a reproducible process.

^ For the time being, we could consider publishing a separate reproducible image, because the new profile has some properties that we may not want in a standard build:

• panic = "abort": we lose crash info, ideally we remove this - but not sure if this is necessary for reproducible builds.
• overflow-checks = true: this is not usually on, so it should be tested.

lighthouse/Cargo.toml

Lines 301 to 306 in 2b398f0

	[profile.reproducible]
	inherits = "release"
	debug = false
	panic = "abort"
	codegen-units = 1
	overflow-checks = true

Eventually it would be nice to consolidate, but we'd need some further testing.