source-{various}: harden conditional reduction annotations for hard deletes

[Alex-Bair]

Description:

The current conditional reduction annotation of:

if:
  properties:
    _meta:
      properties:
        op: { const: "d" }
then:
  reduce: { delete: true, strategy: merge }
else:
  reduce: { strategy: merge }

also matches when either _meta or op are not present. Meaning, if either of those are absent, the if conditional evaluates to true and the delete: true, strategy: merge in the then branch is applied. That's not what we want; we only want that deletion reduction to be applied when both fields are present and op is "d".

This PR hardens the if check. By requiring _meta and op to be present, the if conditional only evaluates to true when both are present in the document and op is "d":

if:
  required: ["_meta"]
  properties:
    _meta:
      required: ["op"]
      properties:
        op: { const: "d" }
then:
  reduce: { delete: true, strategy: merge }
else:
  reduce: { strategy: merge }

The multitude of snapshot updates are expected due to the additional requireds added to the if/then/else block in discovered schemas.

Notes for reviewers:

For reference on the if/then/else behavior, check out the official JSON schema docs. This callout on that page is relevant:

Because the if schema also doesn't require the "country" property, it will pass and the "then" schema will apply.

I'm not aware of any reported bugs due to the laxer matching behavior, likely because all documents emitted by these connectors have a _meta and _meta/op field present. I'd still like to close the gaps with these conditional reduction annotations so they're better references for future connectors or derivations that need to signal hard deletes via the same conditional reduction annotation.