fix: circular dependency b/w feature and mercury

[mkesavan13]

COMPLETES SPARK-515520

This pull request addresses

The final circular dependency that is left out. This PR cuts off the circular dependency between internal-plugin-mercury and internal-plugin-feature

by making the following changes

• Remove the internal-plugin-mercury dependency from internal-plugin-feature
• On successful connect of webex.mercury.connect event, the mercury object listens to the event_featureToggle
• Whenever this event is called, the handler checks if it has a legitimate envelope and identifies the feature and sends it to feature plugin by calling webex.internal.feature.updateFeature
• This webex.internal.feature.updateFeature is the method that is modified from earlier handleFeatureUpdate call back listener

Change Type

• [x] 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 change)
• [ ] Documentation update
• [ ] Tooling change
• [x] Internal code refactor

The following scenarios where tested

< ENUMERATE TESTS PERFORMED, WHETHER MANUAL OR AUTOMATED >

I certified that

• [x] I have read and followed contributing guidelines

• [x] I discussed changes with code owners prior to submitting this pull request

• [x] I have not skipped any automated checks

• [x] All existing and new tests passed

• [x] I have updated the documentation accordingly

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