[Substrate] Relayers top-up CLI command

[nmlinaric]

Description

We need CLI command that would enable easy top up of all relayers. This command should check balances of all relayers and based on some threshold top-up all relayers addresses that are under threshold.

Implementation details

Follow implementation pattern of already implemented CLI commands.

suggested CLI flags:
--check-only - only check balances, don't top-up
--env - define environment (required flag)

Acceptance Criteria

• Test CLI to top up relayers on multiple networks on testnet
• Update README with instuctions