Matrix results can be displayed in vector charts

What does this MR do?

Related to #223804 (closed)

Matrix results can be displayed in vector charts

When a matrix result is obtained from prometheus, the parsing defines a "values" array with a time range of results.

However, some charts, like the bar chart, can only present an instant vector.

This change enables all matrix type results to be visible on charts that support instant vectors. To do so it picks the last result and presents it as "the" current vector.

This change does not have effect on charts yet, the data will be visible in a follow up MR.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
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• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
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