Avoid mcatalog metric_name non renaming, replace groupby, replace pipe where

[Guilhem Marchand]

• some versions of Splunk incorrectly complain about mcatalog calls with metric_name not renamed
• replace groupby by “by”
• avoid pipe where with direct where

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[Guilhem Marchand]

Fix Issue #61

→ <<cset 0e8db590854a>>