chain-id should be a property

[Adamantios]

The chain-id should be a property in the transaction settlement skill:

https://github.com/valory-xyz/open-autonomy/blob/v0.14.10/packages/valory/skills/transaction_settlement_abci/rounds.py#L248-L250

If the default chain id needs to be used as a fallback, then we can utilize the default chain ID from the params.

The skills that utilize the tx settlement skill should use this property instead of redefining it such as here for example:

https://github.com/valory-xyz/IEKit/blob/v0.9.2/packages/valory/skills/mech_interact_abci/states/base.py#L129-L132