Proposed changes

Update the docs about the AWS IoT Core where the iot:RetainPublish permission was missing which can result in the thin-edge.io bridge being disconnected from the server if the user publishes a retained message directly to the bridge topic.

The existing system test was also extended to include publishing retained messages. The policy change used within the test is included in the robotframework-aws library (hence the bump in the library's version.

Note: The AWS IoT Core policy actions/permissions are detailed here.

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Improvement (general improvements like code refactoring that doesn't explicitly fix a bug or add any new functionality)
• Documentation Update (if none of the other choices apply)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Paste Link to the issue

Checklist

• I have read the CONTRIBUTING doc
• I have signed the CLA (in all commits with git commit -s. You can activate automatic signing by running just prepare-dev once)
• I ran just format as mentioned in CODING_GUIDELINES
• I used just check as mentioned in CODING_GUIDELINES
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Further comments