CLOUDP-225849: Add scaffolding of the openapi cli

[andreaangiolillo]

Ticket: CLOUDP-225849

Description

This PR adds the scaffolding of the openapi cli that we will use to merge OASes. In particular, this PR defines the cli builder and the merge command without any logic.

make build                                                                                                                                          4s  1.21.4  16.18.0
==> Building openapicli binary
go build -ldflags "-s -w -X github.com/mongodb/openapi/tools/cli/internal/version.GitCommit=e5fb49fd94796ca0a81618431d81c38d6ff45f7f -X github.com/mongodb/openapi/tools/cli/internal/version.Version=v0.0.1" -o ./bin/openapicli ./cmd

./bin/openapicli -v                                                                                                                                  1.21.4  16.18.0
openapicli version: next
git version: next
Go version: go1.21.4
   os: darwin
   arch: arm64
   compiler: gc

Next steps

• Open a follow up PR to add the logic of the merge command
• Open a follow up PR to add tests

[gssbzn]

let;s use flags, they are friendlier

[andreaangiolillo]

I will add the logic in a follow-up PR. Out of curiosity, how do you envision the usage of the command when we want to merge multiple specs into the base one? Based on your comment, I was thinking about moving the base spec to a flag and leaving the other as args. What do you think?

[gssbzn]

either same as you have here, first is base or --base --external... or something like that and why flags tend to be friendlier

[gssbzn]