Add tool to generate metrics documentation

[machadovilaca]

What this PR does / why we need it:

This PR adds a tool to automatically generate documentation with information about exposed metrics.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged): Fixes #

Special notes for your reviewer:

Release note:

NONE

[kubevirt-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: machadovilaca

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[sonarcloud[bot]]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
1 Code Smell

No Coverage information
0.0% Duplication

[kubevirt-bot]

@machadovilaca: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-vm-import-operator-e2e-k8s-1.20	20a1c51372e56a88b81a1474ac1440af581011ac	link	true	/test pull-vm-import-operator-e2e-k8s-1.20

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