Proto commits in square/rce-agent

These 10 commits are when the Protocol Buffers files have changed:

Commit:e4c8199
Author:Daniel Nichter

Remove vendor, update go.mod and deps. Update test TLS certs, and add script to regenerate in 2y. Update copyright line.

The documentation is generated from this commit.

Commit:0b77b23
Author:Daniel Nichter

Convert to go mod

Commit:9f95e79
Author:Daniel Nichter

Add CONTRIBUTING. Update README and deps.

Commit:93bce06
Author:Michael Puncel

Upgrade google.golang.org/grpc and github.com/golang/protobuf

Commit:6a2b967
Author:Brian Ip
Committer:Brian Ip

Fix race condition in Stop

Commit:692a3a8
Author:Daniel Nichter

Large refactor based on all feedback

Commit:6256b3d
Author:Daniel Nichter

Rename 'job' to 'command' and remove duplicate 'CommandName'. Use only pb/ structs.

Commit:5dbb4ed
Author:Chris Uzelac
Committer:Chris Uzelac

use go-cmd/cmd for command execution - use `runningJob` type to hold metatadata and do translation between `cmd.Status` and our `pb.JobStatus` - add server function `WaitOnJob` for testing so we don't have to sleep - many TODOs

Commit:b882d0e
Author:Daniel Nichter
Committer:GitHub

Refactor to simpler organization

Commit:e063b0d
Author:Brian Ip

rce-agent: basic client + server