[website] Use .asf.yaml for deploying the webside and documentation.

I'd like to propose changing the way the site/documentation is deployed at https://avro.apache.org.
Currently it comes from Subversion: http://svn-master.apache.org/repos/asf/avro/site/publish
I suggest to make use of .asf.yaml (https://cwiki.apache.org/confluence/display/INFRA/Git+-+.asf.yaml+features#Git.asf.yamlfeatures-WebsitedeploymentserviceforGitrepositories) instead.
 
With the new approach it will be possible to:
1) deploy the docs from master to https://avro.staged.apache.org
2) deploy latest release, e.g. 1.11.1, to https://avro.apache.org
3) deploy older versions, e.g. 1.10.0, to https://avro.apache.org/1.10.0/
 
 
We will either redirect to the old versions of the docs from Subversion or create Git branches/tags and copy the content.