[BCI-1477] Implement cosmos specific txn type for generic txm

[yongkangc]

This PR implements implements chain specific transaction type based on the generic Transaction manager transaction interface.

Context:

• In order for cosmos to make use of generic txm logic, it requires to implement the TxRequest type and encoding/decoding methods are needed.
• The EVM has a similar implementation here: https://github.com/smartcontractkit/chainlink/blob/7b57ad4c15a2286377ba8cb8775d6c7aa2796251/core/chains/evm/txmgr/models.go#L16-L17

Changes:

• bumping chainlink-relay to make use of the generic Txn Types in the PR https://github.com/smartcontractkit/chainlink-relay/pull/154
• implemented chain specific transaction types and encoding/decoding methods.
• tests

Note:

• Not sure if we would want to merge this, as this PR is dependent on Txn-types on chainlink-relay in the PR https://github.com/smartcontractkit/chainlink-relay/pull/154. However we are still in the middle of persistence layer proposal, and sqlx dependency has yet to be extracted out. See comment for the discussion.
  • Might have to consult @aalu1418 for path forward.

References:

• Design docs
• Tickets: https://smartcontract-it.atlassian.net/browse/BCI-1477

[yongkangc]

The Staging branch has been changed to cosmos-generic-txm-staging