Misconfigurations in outbound push config result in unexpected behavior.

[witash]

Describe the bug
Misconfigurations in outbound push config result in unexpected behavior.
If a mapping value does not have type "string" and is not an Object with a property "expr", this is a misconfiguration; it is not defined what the mapping should do.
What it actually does is include the entire document in the mapped field in the payload.

To Reproduce

1. create an outbound push config with a mapping field that is neither a string nor an Object with property "expr", e.g.

...
"outbound": {
    "relevant_to": "doc.type == 'data_record'",
    "mapping": {
        "example_path": {
            "not_expr": "[{ \"example\": doc.phone }]",
            "optional": true
        }
    }
}

2. create any document that will trigger the outbound push (any report with the example above)
3. Look at the mapped field in the outbound push body ("example_path" in the example above); if will contain the entire document

Expected behavior
If the configuration has a mapping value that is undefined, mapping should raise error OutboundError(Mapping error for '${key}/${dest}' JS error on source document: '${doc._id}': ${err}); similar to what happens with other config misconfigurations.
This alerts users to fix the configuration instead of allowing the outbound push to silently continue with a payload that is probably not what they intended.

[mrjones-plip]

Thanks so much for chasing this down Diana! Do you know what versions this applies to?