Use `serverless-offline-ssm` plugin

Purpose

This change adds the serverless-offline-ssm plugin so that running the Quickstart locally does not require AWS credentials.

Linked Issues to Close

Approach

The QuickStart already supports local development via the serverless-offline and serverless-local-s3 plugins and the dev.ts script. However, when running locally, the uploads and app-api services can't start because of a dependency on SSM parameters.

This change adds the serverless-offline-ssm plugin to remove this dependency. The plugin is configured to only take effect for the local stage, and provides default values for the SSM variables for the uploads and app-api services directly, rather than reading them from AWS.

Learning

Assorted Notes/Considerations

Testing: I ran dev.ts local and confirmed that all services started without error, even without AWS credentials in the local environment.

Pull Request Creator Checklist

[ ] This PR has an associated issue or issues.
[ ] The associated issue(s) are linked above.
[ ] This PR meets all acceptance criteria for those issues.
[ ] This PR and linked issue(s) are adequately documented
[ ] This PR and linked issues(s) are a complete description of the changeset; an individual or team should be able to understand the issue(s) and changes by reading through this PR and it's links, with no further interaction.
[ ] Someone has been assigned this PR.
[ ] At least one person has been marked as reviewer on this PR.

Pull Request Reviewer/Assignee Checklist

[ ] This PR has an associated issue or issues.
[ ] The associated issue(s) are linked above.
[ ] This PR meets all acceptance criteria for those issues.
[ ] This PR and linked issue(s) are adequately documented
[ ] This PR and linked issues(s) are a complete description of the changeset; an individual or team should be able to understand the issue(s) and changes by reading through this PR and it's links, with no further interaction.

Enterprise-CMCS / macpro-quickstart-serverless