Use of dashboard fixtures to remove mock data

What does this MR do?

Since the introduction of fixtures its possible to remove some mock data from the specs. This refactoring MR removes some mock data that has moved to the json fixture.

Specifically:

• Removes mocks from mock_data.js that is redundant with data in the fixture.
• Creates a new file called fixture_data.js to keep data loaded from the fixture in different formats (mutated by the store vs. as the original JSON).
• Rewrite of (store_utils.js) to hold store manipulation functions (such as adding a metric result).
• Removes some unused localVue instances.

Screenshots

N/A

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• [-] Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team