feat(engine): Use parsed workflow trigger inputs

[topher-lo]

Requires #644 for enum expectations.

Why

• Previously the workflow expects Pydantic model was only used for validation not parsing / model coercion (see distinction in pydantic docs: https://docs.pydantic.dev/1.10/usage/models/ and screenshot below)
• This means defaults in expects weren't injected into the trigger inputs for workflow runs
• Related issue for template actions (feat+fix(engine)!: Support enums and defaults in Action Templates #644) where pydantic model wasn't used to parse args

What changed

• Add multiple parameterized unit tests for trigger inputs with expects (with defaults, without defaults, with enums)
• Added payload to ValidationResult
• Passed validated payload (aka parsed trigger inputs that conforms to expects pydantic model) into execution context.

References