[WIP] LGTM tag classification

[paulfantom]

According to this doc: https://help.semmle.com/lgtm-enterprise/user/help/file-classification.html#built-in-tags we need to classify files to tell LGTM what they are for, this way it can exclude them from alerts.

As you can see, file classification is really a question of identifying the source or purpose of a file, and giving it a meaningful tag. Currently, the built-in tags are: docs, generated, library, template and test.

These tags can then be used to determine which files should have their results hidden. Currently, if a file has any classification (that is, at least one tag), its results are filtered out from results and statistics.

[paulfantom]

Relates to #4259

[paulfantom]

Turns out we need to merge this first for LGTM to kick in :(

[paulfantom]

I am testing various configs in separate repo: https://github.com/paulfantom/netdata-lgtm