Add duplicate header field processing when creating outgoing response (#7207)
Add duplicate header field processing when creating outgoing response (#7207)

Currently when we are copying fields from a generated base response over
to our outgoing response we ignore duplicate fields.  This can remove
entries from headers such as Cache-Control if they come in on multiple
header fields
pbchou/trafficserver,vmamidi/trafficserver,duke8253/trafficserver,SolidWallOfCode/trafficserver,duke8253/trafficserver,duke8253/trafficserver,vmamidi/trafficserver,SolidWallOfCode/trafficserver,bryancall/trafficserver,pbchou/trafficserver,SolidWallOfCode/trafficserver,SolidWallOfCode/trafficserver,SolidWallOfCode/trafficserver,vmamidi/trafficserver,SolidWallOfCode/trafficserver,duke8253/trafficserver,pbchou/trafficserver,bryancall/trafficserver,pbchou/trafficserver,vmamidi/trafficserver,bryancall/trafficserver,SolidWallOfCode/trafficserver,duke8253/trafficserver,vmamidi/trafficserver,bryancall/trafficserver,duke8253/trafficserver,bryancall/trafficserver,pbchou/trafficserver,pbchou/trafficserver,duke8253/trafficserver,vmamidi/trafficserver,bryancall/trafficserver