feat: Add nowrite option to make the tool work with readonly permissions

[jverhoeks]

Description

Add option nowrite to disable the cloudformation creation. This allows the tool to run with readonly permissions

Fixes #178

Type of change

Please delete options that are not relevant, and add any that may be relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Single Account, Single Service and Single Region
• Single Account, Single Service and Multiple Regions
• Single Account, Multiple Services and Single Region
• Single Account, Multiple Services and Multiple Regions
• CrossAccounts, Multiple Services and Multiple Regions

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have tested this change with all regions and services
• Any dependent changes have been merged and published in downstream modules

[kuettai]

Thank you for contributing. However you can use '--ztestmode 1' to do such already. We intend to keep the empty cloudformation stack as part of the execution. We want it to act as "CloudTrail", a footprint or evidence that ServiceScreener (SS) has been executed in that account.

This is particularly important as we have many AWS users joined AWS partner organization. The partner will run SS on behalf of customers. This created a way for users to have footprint about the activity.