Patch v0.29.1 - Properly remove "preserve_to" setting

[djaglowski]

This PR resolves two problems with the last release, both related to the usage of preserve_to in sub-parsers.

1. The setting was not fully removed from the codebase. It was removed from the base parser struct, but other usages of it existed in "sub-parsers". Additionally, many other parsers used it in their tests cases (via sub-parsers).
2. Likewise, the "preservation-by-default" behavior was not applied to sub-parsers. This behavior should be the same for all parsers in order to ensure a simple and clear rule across the board. It is also necessary, as it can be very difficult to preserve a value that is isolated by a json/regex/csv/kv parser, and then immediately consumed by a sub-parser.

[codecov]

Codecov Report

Merging #468 (f9bf52f) into main (86992df) will increase coverage by 0.1%.
The diff coverage is 84.6%.

@@           Coverage Diff           @@
##            main    #468     +/-   ##
=======================================
+ Coverage   76.8%   76.9%   +0.1%     
=======================================
  Files         85      85             
  Lines       4164    4153     -11     
=======================================
- Hits        3201    3197      -4     
+ Misses       676     672      -4     
+ Partials     287     284      -3     

Impacted Files	Coverage Δ
operator/helper/parser.go	75.0% <ø> (-0.4%)	⬇️
operator/parser/syslog/syslog.go	70.4% <50.0%> (-1.0%)	⬇️
operator/helper/scope_name.go	60.0% <100.0%> (+3.4%)	⬆️
operator/helper/severity.go	77.7% <100.0%> (+5.9%)	⬆️
operator/helper/severity_builder.go	90.2% <100.0%> (-0.1%)	⬇️
operator/helper/time.go	80.4% <100.0%> (+0.9%)	⬆️
operator/helper/trace.go	96.0% <100.0%> (-0.3%)	⬇️
operator/input/tcp/tcp.go	80.0% <0.0%> (+1.5%)	⬆️

[djaglowski]

This patch was unplanned, but migrating the codebase over to contrib is going to take a little while yet. (see comment here) As a result, I think that cutting a patch release here makes sense. Hopefully this is the only one necessary.