chore: Create contract subscription for existing webhook

[arcoraven]

PR-Codex overview

This PR enhances the addContractSubscription functionality by introducing a new optional webhookId parameter, allowing users to either specify an existing webhook or create a new one using a webhookUrl. It improves error handling and ensures proper webhook management.

Detailed summary

• Added shortenAddress import from thirdweb/utils.
• Introduced webhookId as an optional parameter in the request body schema.
• Implemented logic to retrieve an existing webhook or create a new one based on webhookId or webhookUrl.
• Enhanced error handling for webhook retrieval/creation.
• Updated createContractSubscription to use the determined webhookId.

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