SES fromArn is configurable via properties Fixes GH-1025

[thomas-burko]

:loudspeaker: Type of change

• [ ] Bugfix
• [ ] New feature
• [x] Enhancement
• [ ] Refactoring

:scroll: Description

See https://github.com/awspring/spring-cloud-aws/issues/1025

:bulb: Motivation and Context

https://github.com/awspring/spring-cloud-aws/issues/1025

:green_heart: How did you test it?

Subclassed JavaMailSender used it in my production environment.

:pencil: Checklist

• [x] I reviewed submitted code
• [x] I added tests to verify changes
• [x] I updated reference documentation to reflect the change
• [x] All tests passing
• [x] No breaking changes

:crystal_ball: Next steps