Make default timezone location configurable in timestamp parser

[djaglowski]

Please check that the PR fulfills these requirements

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
• Add a changelog entry (for non-trivial bug fixes / features)
• CI passes

[djaglowski]

Log Files	Logs / Second	CPU Avg (%)	CPU Avg Δ (%)	Memory Avg (MB)	Memory Avg Δ (MB)
1	1000	1.862113	+0.17242038	123.61543	+2.5278778
1	5000	6.8450036	+0.6897087	133.35332	+0.42390442
1	10000	12.069458	-0.017027855	140.45851	+2.629303
1	50000	60.22673	+3.9499168	176.24191	+5.6299744
1	100000	115.708626	+1.7113342	219.93158	-11.488678
10	100	2.4310963	+0.034453154	126.999596	+0.23976135
10	500	7.172582	-0.15518808	135.24461	-1.0177765
10	1000	13.414066	-0.48309422	141.79135	-1.3133087
10	5000	63.652206	-0.40102386	185.11989	+0.38362122
10	10000	122.21229	-6.756035	219.00996	-7.865982

[codecov]

Codecov Report

Merging #241 (e7d87f8) into master (cb89ebc) will decrease coverage by 0.27%.
The diff coverage is 73.33%.

@@            Coverage Diff             @@
##           master     #241      +/-   ##
==========================================
- Coverage   71.44%   71.16%   -0.27%     
==========================================
  Files         101      101              
  Lines        5542     5552      +10     
==========================================
- Hits         3959     3951       -8     
- Misses       1160     1176      +16     
- Partials      423      425       +2     

Impacted Files	Coverage Δ
operator/helper/time.go	76.16% <73.33%> (-1.15%)	⬇️
operator/flusher/flusher.go	84.00% <0.00%> (-4.00%)	⬇️
operator/builtin/output/otlp/otlp.go	61.73% <0.00%> (-3.70%)	⬇️
operator/builtin/input/tcp/tcp.go	67.21% <0.00%> (-3.28%)	⬇️
operator/builtin/output/forward/forward.go	56.52% <0.00%> (-2.90%)	⬇️
operator/builtin/input/file/reader.go	65.06% <0.00%> (-2.41%)	⬇️
operator/builtin/input/file/file.go	73.97% <0.00%> (-2.05%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update cb89ebc...e7d87f8. Read the comment docs.