[PWGLF] Move the K1 micro analysis selection into PWGLF/Core/K1AnalysisMicroCore.h

Split the K1(1270) microtrack histogram task into a reusable core header
and a thin workflow, so that other K1 workflows can share one selection
and candidate loop implementation instead of copying it.

- PWGLF/Core/K1AnalysisMicroCore.h (new): event, track, PID, secondary
  and candidate configurable groups (no group prefix, so all JSON keys and
  defaults are unchanged), the track quality/PID stages, the quantised
  DCA/nSigma grid checks, the sibling-based truth classification, the
  unordered triplet loop with its selection cache and cut-flow
  histograms, and the histogram registration. No using-directives, no
  runDataProcessing.h.
- k1AnalysisMicro.cxx: struct K1AnalysisMicro now owns the configurable
  groups, the histogram registry and the process functions, and calls the
  core. Process switches, configurable names/defaults, histogram names and
  the selection are unchanged.

Author: BongHwi