Add Support for DD_TRACE_SAMPLING_RULES

[sabrenner]

What does this PR do?

Adds support for the environment variable DD_TRACE_SAMPLING_RULES, and appropriate documentation. Removes this feature from options.experimental.sampler, along with sampleRate and rateLimit. sampleRate can still be specified in options.ingestion, and samplingRules as well as rateLimit can also be set on the options path directly (or in their respective environment variables).

Motivation

Consistency in naming conventions and sampling among tracers for other languages.

[codecov[bot]]

Codecov Report

Merging #2202 (1197caa) into master (1197caa) will not change coverage. The diff coverage is n/a.

:exclamation: Current head 1197caa differs from pull request most recent head 8afb589. Consider uploading reports for the commit 8afb589 to get more accurate results

@@           Coverage Diff           @@
##           master    #2202   +/-   ##
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  Coverage   93.01%   93.01%           
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  Files         239      239           
  Lines        9237     9237           
=======================================
  Hits         8592     8592           
  Misses        645      645           

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[github-actions[bot]]

Overall package size

Self size: 2.73 MB Deduped: 30.36 MB No deduping: 31.02 MB

Dependency sizes

name	version	self size	total size
@datadog/pprof	1.0.2	8.74 MB	14.46 MB
@datadog/native-metrics	1.4.2	6.61 MB	7.04 MB
@datadog/native-appsec	1.2.1	5.1 MB	5.43 MB
cidr-matcher	2.1.1	224.94 kB	451.39 kB
opentracing	0.14.7	194.81 kB	194.81 kB
@datadog/sketches-js	2.1.0	109.9 kB	109.9 kB
lodash.sortby	4.7.0	75.76 kB	75.76 kB
semver	5.7.1	61.58 kB	61.58 kB
ignore	5.2.0	48.87 kB	48.87 kB
import-in-the-middle	1.3.1	30.44 kB	34.91 kB
istanbul-lib-coverage	3.2.0	29.34 kB	29.34 kB
retry	0.10.1	27.44 kB	27.44 kB
lodash.uniq	4.5.0	25.01 kB	25.01 kB
limiter	1.1.5	23.17 kB	23.17 kB
lodash.kebabcase	4.1.1	17.75 kB	17.75 kB
lodash.pick	4.4.0	16.33 kB	16.33 kB
crypto-randomuuid	1.0.0	11.18 kB	11.18 kB
diagnostics_channel	1.1.0	7.07 kB	7.07 kB
path-to-regexp	0.1.7	6.78 kB	6.78 kB
koalas	1.0.2	6.47 kB	6.47 kB
methods	1.1.2	5.29 kB	5.29 kB
module-details-from-path	1.0.3	4.47 kB	4.47 kB

_{🤖 This report was automatically generated by heaviest-objects-in-the-universe}