RFP: xDS conformance test suite

# Request for Proposals

The Envoy maintainers and CNCF are soliciting proposals for vendors to build an xDS conformance test suite. The statement-of-work (SoW) is provided [here](https://docs.google.com/document/d/17E3k4fGJedVISCudrW4Kgzf89gvIIhAdZnJmo6pMVlA/edit).

The RFP will be open from 2020-9-17 to 2020-10-8.

Vendors should submit a staged proposal for building the test suite, with independent cost estimates for version 0.5, version 1.0 and version 2.0. Version 3.0 is out-of-scope for this RFP. Vendors may optionally choose to only provide estimates for a subset of versions, e.g. version 0.5 and version 1.0 only.

Vendors should communicate feedback on the proposal and request clarification from either @envoyproxy/api-shepherds or in the SoW as a doc comment.

Vendors who are not well-known to the Envoy maintainer community should submit details including CVs/resumes, evidence of past contributions to Envoy/xDS and/or evidence of similar test framework engineering efforts. We encourage only vendors who have serious engagement with Envoy/xDS or protocol conformance test frameworks to submit bids.

Please submit bids to envoy-maintainers@googlegroups.com.

The Envoy API shepherds will convene after the RFP closes on 2020-10-8 and notify vendors within 2 weeks.