Stream entrypoint logs, distinguish app vs system logs, colorize

[mitchellh]

This modifies the entrypoint to send its logs to the Waypoint server and make them available via waypoint logs.

I did this because as I was finishing up config syncing I realized its critical to be able to see any errors in syncing config and its a huge PITA on most systems that aren't local Docker.

The server API was modified to take a "source" with each log entry so we can tag app logs vs entrypoint logs vs. future other logs differently. This is fully backwards compatible since we just added a field and we default it to "app" scope for the zero (unset) value.

For the log streaming, we only send Info and above level logs to the stream. This currently isn't configurable. However, we still log trace level logs to the default (stderr) output. So if things are going really wrong and we need to debug further, users can still view their pod logs or container logs or whatever and grab more detailed logs. In reality for a user, any issues will be logged Info, Warn, or Error, so they'll show up in waypoint logs.

I also made it so waypoint logs colors the sources differently. It looks like this:

[briancain]

👍 looks good to me! I like the ux and color updates 🎨

[evanphx]

One minor comment about atomic pointer alignment.

[mitchellh]

This just wasn't used so I deleted it.