feature: Add security group as input

[fatbasstard]

This PR adds the capability to pass a security group instead always creating one with the Lambda itself.

Reasoning
Currently, for every Lambda it's own security group is created (when running in a VPC), with just a simple Egress. Downside it that this can cause limits being hit:

• https://aws.plainenglish.io/dealing-with-you-have-exceeded-the-maximum-limit-for-hyperplane-enis-for-your-account-223147e7ab64
• https://docs.aws.amazon.com/lambda/latest/dg/foundation-networking.html

AWS is not happy with updating these limits BTW...

The change
By allowing to pass along the security group, it's possible to reuse SG's (e.g. between similar Lambda's) and prevent the limitation issue.

Update
Passing a single SG as a string causes new deployments (where the SG and the Lambda are deployed in the same TF run) to break ("unable to determine..." thing).

Changed into an array (which is the actual settings of a Lambda) so we can use length which works for Terraform.

Kept the "old" output to return the generated ID, added a new for all the ID's.

With this it's fully backwards compatible and just adds a feature (to pass your own SG's)

[github-actions]

Terraform Format and Style 🖌success

Terraform Initialization ⚙️success

Terraform Lint 📖success

Terraform Validation 🤖success

Validation Output

Success! The configuration is valid.

[stefanwb]

Hi! In the current state of the PR if you specify both a security_group_id and security_group_egress_rules TF will fail on resource "aws_vpc_security_group_egress_rule" "default".

Also the variable security_group_name_prefix should not be set when security_group_id is set.

Could you add validation to security_group_id and check if security_group_egress_rules or security_group_name_prefix are set?

Some changes made

[stefanwb]

Small change requested