Proposed changes

After #10029 was merged I realised it would be nice to have a better API interface for the shared store service. Even though it is an internal API that users don't interact with it will make code more and better to read if we stay compliant with common API design patterns.

Types of changes

• Polish (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)
• Documentation update

Checklist

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• I have added proper type definitions for new commands (if appropriate)

Further comments

n/a

Reviewers: @webdriverio/project-committers