Add some more properties

[soerenmartius]

Changelog

• Output variables as a map instead of single outputs
• Add 'reserved_concurrent_executions' and 'dead_letter_config_target_arn'
• Add vpc_config block to the aws_lambda_function resource.
• Add 'layers' and 'kms_key_arn'

[soerenmartius]

Lgtm.. will review a bit deeper at a later time..

shall we leave this PR open for a proper review or merge and adjust later?

[mariux]

Not yet approved ;) so keep it open.. ;) looks good so far..