Multiple Init Params Support

[azriel91]

Currently WorkspaceInit, ProfileInit, and FlowInit are single types.

Implementors may wish to take in init parameters that are relevant to different ItemSpecs, and so each init parameter needs to be able to be mapped to multiple different data types and inserted as resources.

Use cases:

• Parameters from the user during CLI usage -- these should be serialized and stored, and deserialized for subsequent commands.
• Tests may want to insert params for each item spec -- not necessarily to be serialized, but doesn't hurt if they are.

Options:

• Store a TypeMap per workspace / profile / flow, then move the resources across to the CmdContextBuilder resources map.

  We need to be able to deserialize parameters from the *_init.yaml files, so taking in arbitrary with_*_init(..) doesn't work.

• Still take a single type per workspace / profile / flow, but also take a mapper that maps from that init param type to different data types and inserts them into the resources map.

• Also have with_resource(..) methods in CmdContextBuilder for things that don't need to be serialized/deserialized -- saves people from needing to access Resources after building the context and then insert.