Allow customisation of additional template fields

[seancaffery]

We need to run two instances of the sync for different Google accounts. There are naming conflicts when trying to do this with two instances in the same account. I've added some additional parameters that allow us to avoid the conflicts.

• Allow override of the Cloudwatch log group name
• Allow a suffix to be added to the IAM role
• Allow override of the Lambda function name

I'm not committed to doing it in this exact way but I do need some way to customise the mentioned fields. Thanks :)