IAV-989/feat(credential): add INSTAGRAM_HEADER_AUTH credential type support

Summary

Adds support for a new credential type INSTAGRAM_HEADER_AUTH, designed for Instagram integrations that rely on HTTP header-based authentication rather than the standard Facebook Graph API OAuth flow.

Changes

• CredentialType enum: Added INSTAGRAM_HEADER_AUTH entry
• mapCredentialTypeToN8NType(): Maps INSTAGRAM_HEADER_AUTH → httpHeaderAuth
• mapN8NTypeToCredentialType(): Detects Instagram header auth credentials by checking for instagram + header + auth in the type string

Motivation

Some Instagram API integrations (e.g. private/business APIs) require custom header auth rather than OAuth2 via the Facebook Graph API. This new type allows those credentials to be managed distinctly from the standard INSTAGRAM type.

Testing

• Create a credential with type INSTAGRAM_HEADER_AUTH via the API
• Verify it is stored and replicated correctly across N8N instances
• Verify reverse mapping works when reading back from N8N

Notes

No breaking changes. Existing INSTAGRAM credentials are unaffected.

Related Issues

Closes IAV-989