Block source for aggregator (#3097)

## Linked Issues/PRs
<!-- List of related issues/PRs -->
https://github.com/FuelLabs/fuel-core/issues/3087

## Description
<!-- List of detailed changes -->

This adapter holds two services of its own:
- Importer Task
- Sync Task

The importer task is responsible for getting new blocks as they are
produced. This will run in perpetuity.

The sync task will just find any blocks that have already been produced
and won't be streamed through the importer. This will run on startup,
but should hopefully finish very quickly. We decided not to have the
sync task be blocking, like we might do on more critical systems,
instead it runs once all the services are started to not block anyone
else.

## Checklist
- [ ] Breaking changes are clearly marked as such in the PR description
and changelog
- [ ] New behavior is reflected in tests
- [ ] [The specification](https://github.com/FuelLabs/fuel-specs/)
matches the implemented behavior (link update PR if changes are needed)

### Before requesting review
- [ ] I have reviewed the code myself
- [ ] I have created follow-up issues caused by this PR and linked them
here

### After merging, notify other teams

[Add or remove entries as needed]

- [ ] [Rust SDK](https://github.com/FuelLabs/fuels-rs/)
- [ ] [Sway compiler](https://github.com/FuelLabs/sway/)
- [ ] [Platform
documentation](https://github.com/FuelLabs/devrel-requests/issues/new?assignees=&labels=new+request&projects=&template=NEW-REQUEST.yml&title=%5BRequest%5D%3A+)
(for out-of-organization contributors, the person merging the PR will do
this)
- [ ] Someone else?

---------

Co-authored-by: Aaryamann Challani <43716372+rymnc@users.noreply.github.com>
Co-authored-by: Green Baneling <XgreenX9999@gmail.com>