op-service: Go service templating

The current services in the monorepo are not templated, but do follow similar patterns. Refactoring existing ones will be a big effort, but services should not be difficult to set up.

We have two options:
1. introduce service templating in Go, refactor to use the template as much as we can over time, to not de-dup code.
2. keep the service patterns similar.

Option 2 is the more viable solution for now. A good example of a service scaffolding can be found here: https://github.com/ethereum-optimism/optimism/pull/14270

Long-term we do want to adopt option (1) for more dry code.