Restructure workflows steps

[PawelPeczek-Roboflow]

Description

This is new version of Execution Engine for workflows. Shipped changes:

• workflows blocks with state
• workflows blocks as standalone modules with interface that makes it possible to fully describe the behaviour of block and manifest it externally via OpenAPI 3.0 and custom metadata that are drawn automatically from the code
• EE compatible with new self-describing blocks
• Blocks possible to control flow of workflow execution - hence Condition is no longer the only, hard-coded block with that capability
• loading external blocks from workflows plugins
• state of workflow block can be initialised automatically by EE
• auto-generated docs with help of @SkalskiP
• API to get extensive descriptions of loaded blocks dynamically (with information what is connectable to what)
• API to get dynamic step outputs
• API to validate workflow

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• This change requires a documentation update (shipped with PR)

How has this change been tested, please provide a testcase or example of how you tested the change?

• automated unit tests for workflows running in CI for grid of Python versions
• automated integration tests for workflows running in CI for grid of Python versions
• integration tests for new endpoints in API
• deployed and tested at staging env

Any specific deployment considerations

• deployment to prod to be aligned with UI changes by @hansent

Docs

• Docs updated? What were the changes:
• auto-generated kinds: https://inference.roboflow.com/workflows/kinds/
• auto-generated blocks docs: https://inference.roboflow.com/workflows/blocks/ thanks to @SkalskiP
• new "understanding workflows" page: https://inference.roboflow.com/workflows/understanding/
• updated contrib guide: https://inference.roboflow.com/workflows/workflows_contribution/

[grzegorz-roboflow]

Also block_type may go out of sync with type

[grzegorz-roboflow]

could do this same way as you have done a few lines above

    kinds_names = [k.name for k in declared_kinds]
    if len(declared_kinds) != len(set(declared_kinds)):
        raise

[PawelPeczek-Roboflow]

yes, but my point was to deliver problematic elements in error message to provide more context