Auto-release all clients when publishing with Maven

This property is covered in [the
docs](https://central.sonatype.org/publish/publish-maven/#nexus-staging-maven-plugin-for-deployment-and-release).
It also allows for a manual review opportunity... but given that we don't do
that, and that we test first, let's not go there.

clients/pom.xml

@@ -86,6 +86,7 @@
         <configuration>
           <serverId>ossrh</serverId>
           <nexusUrl>https://s01.oss.sonatype.org/</nexusUrl>
+          <autoReleaseAfterClose>true</autoReleaseAfterClose>
         </configuration>
       </plugin>
     </plugins>

pkg/config/config.go

@@ -388,6 +388,11 @@ type Config struct {
 		Enabled       bool          `mapstructure:"enabled"`
 		FlushInterval time.Duration `mapstructure:"flush_interval"`
 	} `mapstructure:"usage_report"`
+	Plugins map[string]struct {
+		Name   string
+		Path   string
+		Config map[string]interface{}
+	}
 }
 
 func NewConfig(cfgType string) (*Config, error) {