feat: Add support for managed_instances_provider argument

[bryantbiggs]

Description

Motivation and Context

• Resolves ECS Managed Instances #359

Breaking Changes

How Has This Been Tested?

• I have updated at least one of the examples/* to demonstrate and validate my change(s)
• I have tested and validated these changes using one or more of the provided examples/* projects

• I have executed pre-commit run -a on my pull request

[bryantbiggs]

Still working on finding a solution for:

• the timing between the ECS managed instances capacity provider being ready and downstream services
• why services need to explicitly list the ECS managed instances capacity provider instead of using the default if one is not explicitly provided

New APIs, fun times ... fun may vary