Loki: Fix parser hint for extracted labels which collide with stream labels

[slim-bean]

This is one possible solution but without knowing this code real well I suspect it's not the best solution.

[codecov-io]

Codecov Report

Merging #3380 (3847305) into master (287244d) will increase coverage by 0.41%.
The diff coverage is 66.48%.

@@            Coverage Diff             @@
##           master    #3380      +/-   ##
==========================================
+ Coverage   62.44%   62.86%   +0.41%     
==========================================
  Files         200      205       +5     
  Lines       17101    17401     +300     
==========================================
+ Hits        10679    10939     +260     
- Misses       5457     5479      +22     
- Partials      965      983      +18     

Impacted Files	Coverage Δ
cmd/docker-driver/main.go	0.00% <0.00%> (ø)
cmd/migrate/main.go	5.40% <0.00%> (ø)
cmd/querytee/main.go	0.00% <0.00%> (ø)
pkg/chunkenc/memchunk.go	68.10% <0.00%> (ø)
pkg/distributor/http.go	0.00% <0.00%> (ø)
pkg/ingester/stream.go	70.86% <0.00%> (ø)
pkg/ingester/tailer.go	43.80% <0.00%> (ø)
pkg/logcli/client/client.go	5.50% <0.00%> (-0.06%)	⬇️
pkg/logcli/query/query.go	34.80% <0.00%> (ø)
pkg/logcli/query/tail.go	0.00% <0.00%> (ø)
... and 73 more