Allow application to assign a user wallet with new chain

[Nirajsah]

After creating a new game chain, users is required to manually assign the Message_ID and associated public key to their wallets. Without this assignment, users cannot access the chain for operations or queries.

Requirements:

• Message_ID: Value returned when creating a new chain
• PUB_KEY: Public key used during chain creation (two different keys in this case)

Current Manual Process:

linera -w1 assign --key $PUB_KEY_1 --message-id $MESSAGE_ID
linera -w2 assign --key $PUB_KEY_2 --message-id $MESSAGE_ID

Before assigning (wallet_1):

After assigning (wallet_1):