Standalone joystream/node docker image

[mnaamani]

Package the mainnet chainspec file with the docker image for joystream/node to make it simpler to deploy without having to provide it separately.

Some github actions are failing because the github runner is running out of space, a fix is available in this PR https://github.com/Joystream/joystream/pull/4804 so maybe we can merge that first

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1 Ignored Deployment

| Name | Status | Preview | Updated (UTC) | | :--- | :----- | :------ | :------ | | **pioneer-testnet** | ⬜️ Ignored ([Inspect](https://vercel.com/joystream/pioneer-testnet/3TaGSpD3Y2YUhdo4DdeKaMauhrBQ)) | | Jul 20, 2023 8:21pm |