Extension of the BaseOS to use Custom AMI

**Is your feature request related to a problem? Please describe.**
We would like to use our custom AMI (variation of Linux) as the base OS, which seems to be not supported in RES currently.

**Describe the solution you'd like**
I understand this is not supported by RES currently, is there a plan to support this? Or can you provide some guidance on what we need to do in order to achieve this? We do not necessarily need all the features of RES like SW stack install and new AMI creation, is there a minimum set of requirements for an AMI to be RES compatible?

**Describe alternatives you've considered**

**Additional context**
We are evaluating if RES can be used for our solution, currently trying to setup demo first.

Start by reviewing how RES currently provisions and validates its base AMI, then compare those requirements with the requested custom Linux AMI. Define the minimum compatibility requirements and whether reduced functionality such as omitting software-stack installation and new AMI creation can be supported; document the guidance or scope needed for a concrete implementation.

Written by the indexing model from the issue text.