feat: add custom header support for resend, brevo and sendgrid #7216

Job	Run time
Dependency review	7s
Spell check	9s
Get Affected Packages	2m 17s
Build Docker API (novu/api)	38m 15s
Build Docker API (novu/api-ee)	36m 59s
Unit Test Libs	5m 46s
Unit Test Packages	10m 31s
Unit Test Providers	44m 10s
Validate OpenAPI	6m 11s
Unit Test (@novu/worker)	4m 50s
Unit Test (@novu/api)	4m 46s
Unit Test (@novu/inbound-mail)	4m 52s
Unit Test (@novu/webhook)	4m 51s
Unit Test (@novu/ws)	4m 49s
Test Widget Cypress / e2e_widget	16m 27s
Test Web Cypress / e2e_web	43m 22s
Test Web Cypress / component_web	8m 27s
Test API (novu/api) / Check if the secret exists or not.	0s
Test API (novu/api-ee) / Check if the secret exists or not.	1s
Test API (novu/api) / Test E2E	0s
Test API (novu/api-ee) / Test E2E	5m 28s
	4h 2m 18s

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