3. Add docs for stack deployment runs and steps apis

[mrinalirao]

What
Note: The following Stacks PRs need to be approved first and in the following order:

#471
#480

This PR adds API docs for stack deployment runs and stack deployment steps.
https://hashicorp.atlassian.net/browse/TF-26297

NOTE: This PR will remain in draft as this cannot be merged before stacks goes GA.
The API documentation has been divided into multiple PRs to simplify the review process. As each of these PRs is approved, it will be merged into mr/stacks-api-ga branch.

API's introduced in this PR:

1. GET /stack-deployment-groups/{stack_deployment_group_id}/stack-deployment-runs
2. GET /stack-deployment-runs/{stack_deployment_run_id}
3. POST /stack-deployment-runs/{stack_deployment_run_id}/approve-all-plans
4. POST /stack-deployment-runs/{stack_deployment_run_id}/cancel
5. GET /stack-deployment-runs/{stack_deployment_run_id}/stack-deployment-steps
6. GET /stack-deployment-steps/{stack_deployment_step_id}
7. GET /stack-deployment-steps/{stack_deployment_step_id}/stack-diagnostics
8. POST /stack-deployment-steps/{stack_deployment_step_id}/advance
9. POST /stack-deployment-steps/{stack_deployment_step_id}/fail

[aaabdelgany]

I think these will need to be reworked - I expect that they will be moved under the DeploymentStep model. We should leave this comment up so we can double check before GA