Add original metric in String to the Metric object

[im-konge]

Description

Because we are checking the existence of some metric using regexes, it would be worth having the full/original metric in String stored inside the Metric object.
That way we can also see from what was the particular metric object parsed.

This PR adds stringMetric variable to the Metric object, which will contain exactly this value. Because it enhances the default constructor, the constructors (and the creation of each object) had to be changed as well.

Type of Change

• New feature (non-breaking change which adds functionality)

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit/integration tests pass locally with my changes