Add Github Action for Publishing to Comfy Registry

[robinjhuang]

This PR adds a Github Action (publish-node-action) that will publish an updated version of your custom node to the registry whenever the pyproject.toml file changes. The pyproject.toml defines the custom node version you want to publish (added in another PR).

Action Required:

• Make sure the trigger branch (master or main) in publish.yaml matches the branch you want to use as the publishing branch. It will only trigger when the pyproject.toml gets updated on that branch.
• Create an api key on the Registry for publishing from Github. Instructions.
• Add it to your Github Repository Secrets as REGISTRY_ACCESS_TOKEN.

Please message me on Discord at robinken or join our server server if you have any questions!