feat: allow configuring additional security group rules (#56)

## what
* Follow-up of
masterpointio/terraform-aws-ssm-agent#38
* Allow adding additional security groups rules to primary security
group

## why
* To ensure module users don't necessarily need to create separate
security groups to attach additional rules

## references
* N/A



<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **New Features**
- Added support for specifying additional security group rules via a new
configuration option.
- Upgraded the subnet router module to a newer version for improved
compatibility.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Co-authored-by: yangci <yangciouou@gmail.com>

Author: mhulscher