Provide auto-configuration for SendGrid's Java client

[wilkinsona]

https://github.com/sendgrid/sendgrid-java

[maciejwalkowiak]

I would be happy to contribute this feature. Do you have in mind anything more than registering com.sendgrid.SendGrid bean when properties for Sendgrid username and password are set?

[wilkinsona]

Cool! Thanks.

Beyond username and password, the only thing I had in mind was to explore whether or not proxy configuration could be done from the environment as well.