Update `/graft/subnet-evm/Dockerfile` to accept a GO_VERSION arguement.

[JonathanOppenheimer]

Please:

• Add this file to the list of files in the go.mod comment
• File an issue to update this image to accept a GO_VERSION arg as per the example of avalanchego's Dockerfile so that we avoid having to maintain the version in this file, and make mention of removing the file from the go.mod comment once this is done.

Originally posted by @maru-ava in #4762 (comment)