[Feature]: Support REST-based plugins

[Nadine-H]

Problem

There is currently support for plugins, however it requires building plugin code into the Dstack Docker image, . In addition, in some cases users may need to add their own pre-apply validations and policies (that are not applicable to all dstack users). They cannot do this without having to commit the code into Dstack's codebase.

Solution

Implement a plugin that makes REST calls to a configurable server. This server could be used to offload pre-apply policies or any other customer-specific pre-apply hooks to mutate or reject requests. Mutating requests is useful for injecting cost tracking metadata for example.

Workaround

None

Would you like to help us implement this feature by sending a PR?

Yes