Support webhook signature header

[chaoyaji-cb]

What changed? Why?

• Added the signature header attribute when create webhook
• Adjusted the unit tests and added a webhook factory

Qualified Impact

pry(main)> Coinbase::Webhook.create(network_id:"base-mainnet", notification_uri:"https://realtest.com", event_type:"erc20_transfer", event_filters: [{ contract_address: "0x833589fcd6edb6e08f4c7c32d4f71b54bda02913"}], signature_header: 'example_header')
=> Coinbase::Webhook{id: '66ce48aafa6291d3192f170f', network_id: 'base-mainnet', event_type: 'erc20_transfer', notification_uri: 'https://realtest.com', event_filters: '[{"contract_address":"0x833589fcd6edb6e08f4c7c32d4f71b54bda02913"}]', signature_header: 'example_header'}

pry(main)> tmp.update(notification_uri: 'https://updatedrealtest.com')
=> Coinbase::Webhook{id: '66ce48aafa6291d3192f170f', network_id: 'base-mainnet', event_type: 'erc20_transfer', notification_uri: 'https://updatedrealtest.com', event_filters: '[{"contract_address":"0x833589fcd6edb6e08f4c7c32d4f71b54bda02913"}]', signature_header: 'example_header'}

[cb-heimdall]

✅ Heimdall Review Status

Requirement	Status	More Info
Reviews	✅ 1/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1

Approved review 2264655996 from cb-davidlai is now dismissed due to new commit. Re-request for approval.