build/orca: migrate ORCA protos to cncf/udpa with skeleton build system.

[htuch]

The build system in this PR is largely derived from a minified variant of https://github.com/envoyproxy/envoy/tree/master/api/bazel.

The dependency management is intended to support a minimal standalone build of the UDPA protos and their tests. Consuming projects (e.g. Envoy) will continue to manage dependencies, e.g. gRPC, protobuf, PGV, independently of the repository macros in this PR; over time we may be able to factor out some common concerns.

Signed-off-by: Harvey Tuch htuch@google.com

[htuch]

@mattklein123 @lizan for review. At a bare minimum, we need to add CI to this PR (or an immediate followup) and also check/fix_format. We had to do a lot of forking from Envoy to make this work with Nighthawk, if you have any other better ideas (a common utilities repo?) I'm all ears.

I have an Envoy branch with the WiP for integrating at https://github.com/htuch/envoy/tree/cncf-udap.

[mattklein123]

We had to do a lot of forking from Envoy to make this work with Nighthawk, if you have any other better ideas (a common utilities repo?) I'm all ears.

I think this came up for envoy-mobile also. I think we should definitely look into doing a common utility repo for shared build tools. WDYT?

[mattklein123]

Which parts of this are copied vs. new? I'm trying to figure out what to review here. :)

[htuch]

Basically everything is copied and slimmed down. Maybe an efficient way to do this is to download and just diff individual files against the api/ equivalent in envoyproxy/envoy.

Re: shared repo. Agree. What I can do is work on that as a next step; we can basically do this PR to get a baseline. Then a CI PR to get some basic tests happening and followup with a format PR that introduces the script from a common repo.

[mattklein123]

I'm just going to trust you on the copying and slimming. If you want me to review any specific changes can you let me know and/or just put the original files as an earlier commit in this PR?