simulators/portal: fix race condition in beacon-sync suite

[acolytec3]

The issue:
The portal/beacon-sync test suite currently pulls test data from a live beacon node in order to test syncing the Portal beacon light clients.

The bridge client that retrieves the finalized and optimistic updates continues to pull new updates from the beacon client as long as the test is running.

This can be an issue in the optimistic update test where a new optimistic update is produced every slot.

Only one optimistic update is pushed into the network and the simulator then retrieves a new update from the bridge to compare to when validating the test results.

The solution

Add a parameter to the start method in the BridgeService that tells the bridge whether to continue to retrive new updates from the Beacon Node provider or not. In the the optimistic update test, setting this parameter to false will ensure that we don't accidentally pull a new optimistic update when validating the test result since this is current test only tests for a single update.

[acolytec3]

@njgheorghita see above

[njgheorghita]

Thanks @acolytec3 ! I think this will work great for now. As the suite develops this will probably evolve to allow for more fine-grained control over what content is exactly being gossiped during the test run (aka, gossip multiple optimistic updates and make sure all clients stay up to date, etc.)

If you could just fix the few lint errors in the failing ci run, then everything looks good to me.

Ping @KolbyML for review / merge

[KolbyML]

It looks good, just need CI fixed

[acolytec3]

Lint should be cleaned up. Thanks!

[KolbyML]

looks good