gtm-build/plugin-assembly.xml

<?xml version="1.0"?>
<assembly>
  <id>plugin-assembly</id>
  <includeBaseDirectory>false</includeBaseDirectory>
  <formats>
    <format>zip</format>
  </formats>
  <files>
     <file>
         <source>target/teamcity-plugin.xml</source>
         <outputDirectory>/</outputDirectory>
     </file> 
  </files>
  <moduleSets>
    <moduleSet>
       <useAllReactorProjects>true</useAllReactorProjects>
       <includes>
           <include>org.jetbrains.teamcity:google-tag-manager-server</include>
       </includes> 
       <binaries>
           <outputDirectory>server</outputDirectory>
           <unpack>false</unpack>
           <dependencySets>
               <dependencySet>
                    <includes>
                         <include>*</include>
                    </includes>
               </dependencySet>
           </dependencySets>
       </binaries>
    </moduleSet>
  </moduleSets>
</assembly>