First Relay Validator Registration

[olegshmuelov]

Describe the bug
The bug discovered after implementing this PR
There is an issue in the validator registration process that could lead to registration delays. Specifically, the current logic, which uses the validator's BeaconMetadata.Index in conjunction with registrationSlotInterval for scheduling registration duties, has the unintended potential to postpone a validator’s registration by up to 10 epochs. This delay stems from the way these values are calculated and compared to determine a validator's eligibility for registration at any given slot.

Expected behavior
Register validator to relay in first epoch the node starts

Additional context
Thisi s a regression bug
see commit that removed the first registration logic
the PR the logic was removed from
In addition write tests to validator registration scheduler, covering all scenarios