chore: Allow docletPath to be specified as a user property (#496)

Author: meltsufin

pom.xml

@@ -695,6 +695,7 @@
  <properties>
  <!-- default config values -->
  <docletName>java-docfx-doclet-1.5.0</docletName>
+ <docletPath>${env.KOKORO_GFILE_DIR}/${docletName}.jar</docletPath>
  <outputpath>${project.build.directory}/docfx-yml</outputpath>
  <projectname>${project.artifactId}</projectname>
  <excludeclasses></excludeclasses>
@@ -710,9 +711,7 @@
  <version>3.4.0</version>
  <configuration>
  <doclet>com.microsoft.doclet.DocFxDoclet</doclet>
- <useStandardDocletOptions>false</useStandardDocletOptions>
- <!-- custom config with -Dproperty=value -->
- <docletPath>${env.KOKORO_GFILE_DIR}/${docletName}.jar</docletPath>
+ <useStandardDocletOptions>false</useStandardDocletOptions> 
  <additionalOptions>
  -outputpath ${outputpath} 
  -projectname ${projectname}