feat: add exceptions source file parameter

[gsanchezgavier]

This PR adds the possibility to define the metrics exceptions in a separate file.
This will allow to specify different exceptions for different versions of a particular integration being tested without the need to create a complete spec file.
Using this on newrelic/nri-kubernetes#438 we will define different exceptions files for the different k8s versions. One option to implement this would be to select the except file using an environment variable on the CI

# ...
        - source: "powerdns.yml"
          exceptions_source: ${EXCEPTION_FILE}

[sigilioso]

LGTM 👍 Thanks for taking care of it!

I have a question regarding its usage: if a metric is replaced by another in a particular version, both metrics will be in the spec file and we will need an exception for the new metric in previous versions and another exception for the old metric in new versions, won't we?

[gsanchezgavier]

@sigilioso
I added an example on how to use this on the PR description , not sure if that clarify how it could be used. WDYT

[sigilioso]

@sigilioso I added an example on how to use this on the PR description , not sure if that clarify how it could be used. WDYT

I just was wondering how to face the "metric replacement" use case. With the usage example is even more clearer, thanks! 👍

An example of that use case: if m1 is replaced by m2 in v.X version. Then, using this approach:

• exceptions_file should include an exclusion for m2 when version < v.X
• exceptions_file should include an exclusion for m1 when version >= v.X

[marcsanmi]

LGTM 👍