Unify workspace overflow reporting

[nigoroll]

Expected Behavior

Make it simple to find workspace overflows

Current Behavior

If I am not mistaking (and I probably am overlooking something), one currently needs a monster like this

$ varnishlog -q 'VCL_Error ~ overflow or Error ~ workspace or FetchError ~ workspace or LostHeader'

to find workspace overflows. This really should be simpler.

[nigoroll]

bugwash (phk): Introduce VSL query "macros" for such tasks