Add support for partial reset

## Feature Description

Site Kit has always had the ability to "reset" which deletes all non-persistent site and user data; for all intents and purposes: everything. As the plugin grows in features, this limited option is becoming increasingly heavy-handed as a troubleshooting utility, but currently it is the only way for end users to clear the site credentials which can be necessary in some cases.

Clearing the site credentials allows for restarting the site connection flow. Site credentials are required for reaching the dashboard and plugin settings (as when initially setting up the plugin) but do not affect the function of modules as they are making this safe to do without interrupting the performance of tags in the process.

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## Acceptance criteria

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## Implementation Brief

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### Test Coverage

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## QA Brief

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## Changelog entry

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