[Doc] Clarify usage of official Identity package deployments in documentation

[lautarogiambroni]

Description

Clarify in the Identity documentation that integrators should use the officially deployed Identity packages and do not need to redeploy them. Add clear references to the official deployments across networks.

Reference material

• IOTA Identity documentation
• Identity smart contract deployment references (testnet, devnet, mainnet)

To-do List

• Explicitly state that redeploying Identity packages is not required and not recommended
• Add links to the official Identity package deployments on testnet, devnet, and mainnet
• Explain why official deployments are required for verifiability and trust
• Reinforce this guidance in relevant Identity integration and deployment sections