add SPI for Opentracing implements

[betterjava]

Fixes #2478.

Changes proposed in this pull request:

• add SPI for Opentracing implements .
• add opentracing SPI config for sharding-proxy.

[coveralls]

Pull Request Test Coverage Report for Build 9165

• 11 of 21 (52.38%) changed or added relevant lines in 4 files are covered.
• 3 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.005%) to 64.661%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
sharding-opentracing/src/main/java/org/apache/shardingsphere/opentracing/yaml/config/YamlOpenTracingConfiguration.java	0	2	0.0%
sharding-proxy/sharding-proxy-bootstrap/src/main/java/org/apache/shardingsphere/shardingproxy/Bootstrap.java	0	8	0.0%

Files with Coverage Reduction	New Missed Lines	%
sharding-orchestration/sharding-orchestration-core/src/main/java/org/apache/shardingsphere/orchestration/internal/util/IpUtils.java	3	76.0%

Totals
Change from base Build 246:	0.005%
Covered Lines:	9101
Relevant Lines:	14075

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💛 - Coveralls

[betterjava]

Since I can not find a way to make shardingsphere support Skywalking,jaeger,zipkin by openstracing at the same time,So it make no sence for providing SPI for that. So I close it.