Improve missing ingest processor error

[martijnvg]

This pr fixes two issues:

• Accumulate any potential other processor parse errors before failing instead of failing upon first processor parsing error. This is useful if more than one processor type is unknown, so that the client creating the pipeline knows about all missing processors. Note that suppressed exceptions are not rendered yet on the rest layer. However suppressed exceptions are being serialized in the internal node-to-node layer.
• Attach type and tag header to the error that is thrown when ingest processor isn't available on other ingest nodes.

[talevy]

LGTM