feat(stellar): Add multi-signature wallet support

[zeemscript]

Description

Add support for multi-signature wallets on the Stellar network, enabling transactions that require multiple signatures for approval. This enhances security for high-value transactions and organizational accounts.

Acceptance Criteria

• Support creation of multi-sig wallets with configurable thresholds
• Enable signing and submitting multi-sig transactions
• Track pending multi-sig transactions awaiting signatures
• Provide endpoints for adding/removing signers

Files to modify/create

• src/modules/stellar/multisig.service.ts
• src/modules/stellar/multisig.controller.ts
• src/modules/stellar/dto/multisig.dto.ts
• src/modules/stellar/entities/multisig-transaction.entity.ts

[Peolite001]

I would love to work on this issue