DXCDT-741 Add support for configuring email provider

[acwest]

Auth0 provides integration capabilities with many email providers like sendgrid, mailgun, mandrill etc.
As an extension to this, it now also supports Custom Email Provider which is tied to an action.

🔧 Changes

Add auth0 email provider commands:

• auth0 email provider show
• auth0 email provider create
• auth0 email provider update
• auth0 email provider delete

📚 References

• https://auth0.com/docs/api/management/v2/emails/post-provider
• https://auth0.com/docs/api/management/v2/emails/patch-provider
• https://auth0.com/docs/api/management/v2/emails/get-provider
• https://auth0.com/docs/api/management/v2/emails/delete-provider

🔬 Testing

📝 Checklist

• All new/changed/fixed functionality is covered by tests (or N/A)
• I have added documentation for all new/changed functionality (or N/A)