Add parameter for log retention

[dm3ch]

Is your feature request related to a problem? Please describe.
Now when you are installing SSOSync from AWS App marketplace you are unable to specify log retention period.

Describe the solution you'd like
I would like to have ability to provide existing log group to template or configure retention period of created log group

Describe alternatives you've considered

Additional context

[ChrisPates]

So this spin-it would make this configurable

Explicit log group that refers to the Lambda function

LogGroup:
Type: AWS::Logs::LogGroup
Properties:
LogGroupName: !Sub "/aws/lambda/${Function}"
# Explicit retention time
RetentionInDays: 7

Would need to make it possible to still have Indefinite retention as an option, however un-frugle that may be.

[ChrisPates]

This improvement has been merged in to master and will be released as part of v2.1.x