Fix discovery merging

[psFried]

Discussed in #1268

• Update the Spec response to add a resource_path_pointers field (Phil/discover merge #1291)
• Have agent use the resource_path_pointers, if available, to extract a resource_path for each binding, which is used as an identity to merge the bindings (also Phil/discover merge #1291)
• Update sql batch connectors to set resource_path_pointers in the spec response (Phil/resource path pointers connectors#1083)
• Update other connectors to set resource_path_pointers in the spec response (Phil/resource path pointers airbyte#284 and Phil/resource path pointers connectors#1083)
• Update agent to require that resource_path_pointers always be set

Follow up items from this discussion:

• Deprecate resource_path in Validated response, and add it to Validate request instead
  • This requires threading through the connector spec as part of validation
• If Validated response does include resource_path, validate that it matches the computed one
• The connector_tags handler should validate that resource_path_pointers must not be changed after they're initially set