Fix isChainIDAvailable to also check for the mainchain id

[ishantiw]

Expected behavior

• isChainIDAvailable should return false for mainchainID
• isChainIDAvailable should only be available on mainchain
• It should also check for the networkByte(first byte of the chainID) of the chainID, if not the correct networkByte then return false

Actual behavior

• isChainIDAvailable can return true on sidechain for the mainchain

Steps to reproduce

• Run a sidechain node where mainchain is not registered and query isChainIDAvailable endpoint

Which version(s) does this affect? (Environment, OS, etc...)

v6.0.0-alpha.14