Feature implement get messages paginated and get labels

[Yanhenning]

Types of changes

• [ ] Documentation
• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Description

• Implemented the new method to get all messages with a given filter with pagination
• Implemented a method to get the labels in an easy way
• Fixes tests for GetMessages, the mock was leading into a false positive test

[peril-loadsmart[bot]]

	Warnings
:warning:	It looks like code was changed without adding anything to the Changelog. If you are not sure whether this PR needs a changelog entry you may refer to this confluence page

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