Add missing features to the Solana part of the axelar-contract-deployments repo.

[frenzox]

We agreed that not everything required for the Solana part was needed for testnet tests. Thus, some features where not implemented.
In this issue the goal is to make the Solana part complete and equivalent to what is done for the other chains, including but not necessarily limited to:

• Gas service complete interface
• Operators contract complete interface
• Governance contract complete interface
• Packaging for offline signing
• Solana CI workflow

[frenzox]

The offline signing should be through squads multisig: https://github.com/Squads-Protocol/v4/tree/main/sdk/rs

Edit: Actually, the current offline signing works fine. The squads multisig should be used only where a multisig wallet is required (i.e.: program upgrade).

[frenzox]

Added the Solana CI workflow item. Although I made a start here, it's not priority for testnet.