feat: enable SSM access for runner manager and fleeting

What

• Add custom IAM roles runner nodes
• Add custom Security group for both fleeting and manager

Why

We need to enable SSM to have more visibility on runners to troubleshoot efficiently. We also need custom SG to have more control over networking. This is related to https://gitlab.com/gitlab-com/gl-infra/gitlab-dedicated/team/-/issues/3785

Notes

First of all, @josephburnett @dbickford it is nice to meet you all here! We've been exploring opportunities to enhance the integration between our runner project and GRIT, with a focus on minimizing code duplication and simplifying the process. The primary objective is to achieve a more efficient collaboration between the two systems. I would like to know what are your thoughts or suggestions when we need these changes?