[FLINK-10836] Add repositories and pluginRepositories in root pom.xml

[bjkonglu]

Background

When developer want to build flink project use maven, they may encounter dependency problem which maven can't download dependencies from remote repo.

Analyse

There maybe a way to resolve this problem. That's add remote maven repo in root pom.xml, for example:

<!-- common repositories -->
<repositories>
   <repository>
      <id>alimaven</id>
      <url>http://maven.aliyun.com/nexus/content/groups/public/</url>
   </repository>
   <repository>
      <id>central</id>
      <name>Maven Repository</name>
      <url>https://repo.maven.apache.org/maven2</url>
      <releases>
         <enabled>true</enabled>
      </releases>
      <snapshots>
         <enabled>false</enabled>
      </snapshots>
   </repository>
</repositories>

<!-- common pluginRepositories -->
<pluginRepositories>
   <pluginRepository>
      <id>alimaven</id>
      <url>http://maven.aliyun.com/nexus/content/groups/public/</url>
      <releases>
         <enabled>true</enabled>
      </releases>
      <snapshots>
         <enabled>true</enabled>
      </snapshots>
   </pluginRepository>
   <pluginRepository>
      <id>central</id>
      <url>https://repo.maven.apache.org/maven2</url>
      <releases>
         <enabled>true</enabled>
      </releases>
      <snapshots>
         <enabled>false</enabled>
      </snapshots>
   </pluginRepository>
</pluginRepositories>