Add services pcport command (#2784)

Closes https://github.com/jetify-com/devbox/issues/2783

## Summary

This command returns the port that process-compose is running on. That
makes it more feasible to use the process-compose api in scripting.

For example:
```
pcport=$(devbox services pcport)
curl http://localhost:$pcport/process/good-server | jq ".status, .is_ready"
```

## How was it tested?

With process-compose running:
```
$ dist/devbox services pcport
53173

$ echo $?
0
```

With process-compose stopped:
```
$ dist/devbox services pcport

Error: process-compose is not running or it's config is missing. To start it, run `devbox services up`
source: failed to find projectDir /Users/elliott.hilaire/github.com/elliotthilaire-ca/devbox in config.Instances

$ echo $?
1
```

## Community Contribution License

All community contributions in this pull request are licensed to the
project
maintainers under the terms of the
[Apache 2 License](https://www.apache.org/licenses/LICENSE-2.0).

By creating this pull request, I represent that I have the right to
license the
contributions to the project maintainers under the Apache 2 License as
stated in
the
[Community Contribution
License](https://github.com/jetify-com/opensource/blob/main/CONTRIBUTING.md#community-contribution-license).

## AI disclosure

Claude code assisted in creating this PR.