[Feature]Support configure heartbeat api path of dashboard

[nick-tan]

Describe what this PR does / why we need it

Sentinel transport module does not support configuring API path of dashboard heartbeat.

Does this pull request fix one issue?

Resolves #332

Describe how you did it

add a property item (-Dcsp.sentinel.heartbeat.api.path) to support this

Describe how to verify it

run the test case

Special notes for reviews

[codecov-io]

Codecov Report

Merging #515 into master will decrease coverage by 4.03%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #515      +/-   ##
============================================
- Coverage     41.71%   37.68%   -4.04%     
+ Complexity     1376     1100     -276     
============================================
  Files           304      259      -45     
  Lines          8764     8174     -590     
  Branches       1182     1113      -69     
============================================
- Hits           3656     3080     -576     
- Misses         4662     4700      +38     
+ Partials        446      394      -52

Impacted Files	Coverage Δ	Complexity Δ
...ain/java/com/alibaba/csp/sentinel/util/IdUtil.java	0% <0%> (-100%)	0% <0%> (-6%)
.../sentinel/adapter/dubbo/DubboAppContextFilter.java	0% <0%> (-100%)	0% <0%> (-3%)
...sp/sentinel/adapter/dubbo/AbstractDubboFilter.java	0% <0%> (-100%)	0% <0%> (-4%)
...alibaba/csp/sentinel/adapter/dubbo/DubboUtils.java	0% <0%> (-66.67%)	0% <0%> (-2%)
...nel/adapter/dubbo/SentinelDubboProviderFilter.java	0% <0%> (-64%)	0% <0%> (-2%)
...nel/adapter/dubbo/SentinelDubboConsumerFilter.java	0% <0%> (-57.15%)	0% <0%> (-2%)
...va/com/alibaba/csp/sentinel/init/InitExecutor.java	12.82% <0%> (-47.71%)	2% <0%> (-4%)
...java/com/alibaba/csp/sentinel/util/StringUtil.java	15.38% <0%> (-32.7%)	10% <0%> (-18%)
...src/main/java/com/alibaba/csp/sentinel/Tracer.java	0% <0%> (-31.15%)	0% <0%> (-12%)
...ntinel/slots/block/flow/param/ParameterMetric.java	50% <0%> (-25%)	27% <0%> (-2%)
... and 159 more

---

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 062385f...83af836. Read the comment docs.

[CLAassistant]

All committers have signed the CLA.

[jasonjoo2010]

May I ask that what's the scenario for add a prefix path? Kinds of virtual path?

[sczyh30]

May I ask that what's the scenario for add a prefix path? Kinds of virtual path?

See #332 (though it's rare). Maybe the property item could be used for the arbitrary registry URL path, not just for the prefix.

[sczyh30]

LGTM

[sczyh30]

Thanks for contributing! I'll improve the related code later.