[Connector Builder] Productionize YAML -> UI conversion

[lmossman]

Context

As a result of the POC for this functionality, we are deciding to move forward with implementing this feature.

A PR that lays the groundwork for this can be found here, though it is incomplete: #21142

This is blocked by completion of #21211, so that YAMLs using $refs and $options are able to be converted.

Acceptance Criteria

• YAML manifests that don't encode behavior unsupported by the Connector Builder UI can be converted into UI form values in the Connector Builder UI (by clicking the UI | YAML toggle)
• YAML manifests that do things the Connector Builder UI does not support are rejected during toggling
• YAMLs containing $refs and $options will have those macros resolved and flattened by the endpoint added in Connector builder server endpoint to resolve $refs and $options #21211,