Feature: Reattach to a pipeline run by latest or sequence id

[briancain]

This pull request introduces a new CLI flag for pipeline run to enable the CLI to reattach to an existing pipeline run, either by the latest known run, or by a specific sequence id. It will attempt to reply the job ids in the order defined in the pipeline run message.

Fixes #4010

[xiaolin-ninja]

This feels like it's repeating code that's in the pipeline run command and introduces more maintenance surface and not very dry.

If the key is so the user knows that happens to the run, there is existing waypoint job list -pipeline=<pipeline> -run=<seq> to monitor the state of the job, or waypoint pipeline inspect -run=<seq> for the state of previous runs.

So they could just run job get-stream on the latest job... though I guess if the point is to re-attach them to the stream in real-time... maybe we can figure out how to extract this code so it's not repeated, or add a -reattach command to the existing pipeline run.

[briancain]

@xiaolin-ninja so the main thing this provides is being able to replay or attach to an existing pipeline run (maybe that run was invoked in the UI or automatically by the server and a CLI client wants to follow along, for example).

Using waypoint job get-stream isn't a great user experience. They'd have to figure out what jobs are associated with pipeline runs, and then manually run the get-stream command for every job id. The appeal of something like this PR is only having to provide a pipeline name or run sequence number and replaying or reattaching to a running jobstream for all jobs in execution order.

I'm good with adding a -reattach flag to waypoint pipeline run. The majority of the code in the CLI command on this PR is building up protobufs for requests and sending them over the API so I don't think the duplication is a huge deal, but adding a -reattach to waypoint pipeline run makes sense.

[briancain]

Done via c4d5c28 @xiaolin-ninja !

[xiaolin-ninja]

Tested & looks great!