Use a stable plugin name.

Often the GitHub plugin name has to appear in the Gerrit config
as post-registration or logout URLs.
Making the plugin name fixed and well-known makes this configs more
reliable over time and independent from the different plugin jar
files naming.

Change-Id: I36d04be893065cb1160d39dc1c994f2979d12535

github-plugin/pom.xml

diff --git a/github-plugin/pom.xml b/github-plugin/pom.xml
index 2e92a44..28492d2 100644
--- a/github-plugin/pom.xml
+++ b/github-plugin/pom.xml
@@ -71,6 +71,7 @@
 
                 <Gerrit-ApiType>${Gerrit-ApiType}</Gerrit-ApiType>
                 <Gerrit-ApiVersion>${Gerrit-ApiVersion}</Gerrit-ApiVersion>
+                <Gerrit-PluginName>github-plugin</Gerrit-PluginName>
               </manifestEntries>
             </transformer>
           </transformers>