"Product Tag Counts" metrics report (based on "Product Type Counts")

[tomaszn]

Is your feature request related to a problem? Please describe

I found the "Product Type Counts" metrics page very useful. It is available at the /metrics/product/type/counts path. However, it does not allow further filtering of products on various fields, or generating cross-product type metrics.

Describe the solution you'd like

The most universal form of grouping products in various ways is by assigning them same tags. Each product can have multiple tags assigned, and appear in various tag-based listings.

Therefore, I propose to modify or clone this report, to allow generating such metrics based on groups defined by product tags.

Describe alternatives you've considered

• Grouping products under different product types: would generate much chaos, as users are already used to currently used set up.
• Generate reports in other tools: a lot of domain-specific code would need to be reimplemented, especially when it comes to displaying details of findings.

Additional context

It seems that "Product Type Counts" implementation can be easily generalized for different filtering criteria.
I am attaching a pull request that implements "Product Tag Counts" by reusing (or copying) the existing solution.