chore(doc): fix documentation on cloud.google.com to not show internal classes (#1554)

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Fixes #<issue_number_goes_here> ☕️

If you write sample code, please follow the [samples format](
https://github.com/GoogleCloudPlatform/java-docs-samples/blob/main/SAMPLE_FORMAT.md).

Author: mutianf

pom.xml

@@ -245,6 +245,7 @@
                 </executions>
 
                 <configuration>
+                    <!-- This is the old way of publishing the doc to googleapis.dev -->
                     <doclint>none</doclint>
                     <show>protected</show>
                     <nohelp>true</nohelp>
@@ -318,16 +319,26 @@
                         <artifactId>maven-javadoc-plugin</artifactId>
                         <version>3.4.1</version>
                         <configuration>
+                            <!-- This is the new way of publishing the doc to cloud.google.com -->
                             <doclet>com.microsoft.doclet.DocFxDoclet</doclet>
                             <useStandardDocletOptions>false</useStandardDocletOptions>
                             <docletPath>${env.KOKORO_GFILE_DIR}/java-docfx-doclet-1.5.0.jar</docletPath>
                             <additionalOptions>
                                 -outputpath ${project.build.directory}/docfx-yml
                                 -projectname ${artifactId}
                                 <!-- List of excluded packages as regex, separated by a colon-->
-                                -excludeclasses com\.google\.cloud\.bigtable\.admin\.v2\.internal\.:com\.google\.cloud\.bigtable\.admin\.v2\.BaseBigtableInstanceAdminClient:com\.google\.cloud\.bigtable\.admin\.v2\.BaseBigtableInstanceAdminSettings:com\.google\.cloud\.bigtable\.admin\.v2\.stub\.GrpcBigtableInstanceAdminCallableFactory:com\.google\.cloud\.bigtable\.admin\.v2\.stub\.GrpcBigtableInstanceAdminStub:com\.google\.cloud\.bigtable\.admin\.v2\.stub\.BigtableInstanceAdminStub:com\.google\.cloud\.bigtable\.admin\.v2\.BaseBigtableTableAdminClient:com\.google\.cloud\.bigtable\.admin\.v2\.BaseBigtableTableAdminSettings:com\.google\.cloud\.bigtable\.admin\.v2\.stub\.GrpcBigtableTableAdminCallableFactory:com\.google\.cloud\.bigtable\.admin\.v2\.stub\.GrpcBigtableTableAdminStub:com\.google\.cloud\.bigtable\.admin\.v2\.stub\.BigtableTableAdminStub:com\.google\.cloud\.bigtable\.admin\.v2\.stub\.EnhancedBigtableTableAdminStub:com\.google\.cloud\.bigtable\.data\.v2\.internal\.:com\.google\.cloud\.bigtable\.data\.v2\.BaseBigtableDataClient:com\.google\.cloud\.bigtable\.data\.v2\.BaseBigtableDataSettings:com\.google\.cloud\.bigtable\.data\.v2\.stub\.BigtableStub:com\.google\.cloud\.bigtable\.data\.v2\.stub\.BigtableStubSettings:com\.google\.cloud\.bigtable\.data\.v2\.stub\.GrpcBigtableStub:com\.google\.cloud\.bigtable\.data\.v2\.stub\.GrpcBigtableCallableFactory:com\.google\.cloud\.bigtable\.data\.v2\.stub\.EnhancedBigtableStub:com\.google\.cloud\.bigtable\.data\.v2\.stub\.mutaterows\.:com\.google\.cloud\.bigtable\.data\.v2\.stub\.readrows\.:com\.google\.cloud\.bigtable\.data\.v2\.stub\.metrics\.
+                                <!-- Exclude generating javadocs for internal implementations for admin and data, which
+                                 are under internal/ and .v2.stub/, and exclude all BaseClients and BaseSettings.
+                                 The only exception is we want to keep the javadoc for StubSettings. -->
+                                -excludeclasses com\.google\.cloud\.bigtable\.admin\.v2\.(internal\.|(Base.*).*|stub\.(?!Bigtable.*StubSettings).*):com\.google\.cloud\.bigtable\.data\.v2\.(internal\.|(Base.*).*|stub\.(?!Enhanced.*StubSettings).*)
+                                <!-- Exclude the javadocs for the auto-generated raw protos since we don't expose them.
+                                 The raw protos generated by gapic are under com.google.bigtable. And the public surface
+                                 is under com.google.cloud.bigtable. Also exclude the stats package which is the
+                                 internal implementation for metrics. -->
+                                -excludepackages com\.google\.(bigtable\.v2|bigtable\.admin\.v2|cloud\.bigtable\.stats)
                             </additionalOptions>
                         </configuration>
+
                         <executions>
                             <execution>
                                 <id>aggregate</id>