feat: replace api-common-protos submodule with googleapis

[alicejli]

https://github.com/googleapis/api-common-protos needs to be manually updated, so there is a 2-step process for gapic-showcase to pull in updated api-common-protos. By replacing the api-common-protos submodule with googleapis, it removes one of those steps.

[noahdietz]

You'll want to change these spots to make CI/regen happy:

gapic-showcase/util/compile_protos.go

Line 58 in 1d6dde2

"--proto_path=schema/api-common-protos",

gapic-showcase/util/cmd/release/main.go

Line 68 in 1d6dde2

apiPath := filepath.Join("schema", "api-common-protos", "google", "api")

gapic-showcase/util/cmd/release/main.go

Line 78 in 1d6dde2

longrunningPath := filepath.Join("schema", "api-common-protos", "google", "longrunning")

gapic-showcase/util/cmd/release/main.go

Line 83 in 1d6dde2

rpcPath := filepath.Join("schema", "api-common-protos", "google", "rpc")

[noahdietz]

Awesome, this is definitely better. Just one question

[noahdietz]

Awesome stuff, thank you @alicejli, reducing toil!!