DPL Analysis: support configurables in string expressions

[aalkin]

String expressions can now accept configurables in the following form:

"o2::aod::track::pt > ncfg(float, 0.5, \"pTCut\")"
or
"o2::aod::track::pt > ncfg(float, 0.5, pTCut)"

Or in general
ncfg(type, value, path)
where the type can be uint/int from 16 to 64, float or double, value is the default value, and path is how the configurable appears in JSON, including prefix if needed.

The quotes will be removed automatically if present.

Also fixes the o2TestHistograms.cxx example

[github-actions]

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