Documentation: Forrest 0.9 is being removed from ASF Jenkins

See https://issues.apache.org/jira/browse/INFRA-27339 where Forrest 0.9 is being removed from ASF build systems.

A search of the codebase shows that a patched version by PJ is preferred.

```
./src/documentation/publish-poi-site.txt:35:You also need to install Apache Forrest. Forrest is no longer maintained but PJ has a fork with a few small changes.
./src/documentation/publish-poi-site.txt:36:This is at https://github.com/pjfanning/apache-forrest-0.9
./src/documentation/publish-poi-site.txt:38:You can use the last official Apache Forrest release but you may notice some diffs when you build the site and try to
./src/documentation/publish-poi-site.txt:39:publish it. https://forrest.apache.org/
./src/documentation/publish-poi-site.txt:41:You will need to create an environment variable called FORREST_HOME and set it to match the directory location
./src/documentation/publish-poi-site.txt:42:where you installed Apache Forrest.
```
So the instructions need to be adjusted.

There is a Jenkins file in the repository, but is it current? If so, then this will probably break:

```
./jenkins/create_jobs.groovy:262: env('FORREST_HOME', poijob.windows ? 'f:\\jenkins\\tools\\forrest\\latest' : '/home/jenkins/tools/forrest/latest')
./jenkins/create_jobs.groovy:489: env('FORREST_HOME', xjob.windows ? 'f:\\jenkins\\tools\\forrest\\latest' : '/home/jenkins/tools/forrest/latest')
```

Read src/documentation/publish-poi-site.txt and the ASF INFRA-27339 issue first, then inspect the FORREST_HOME entries in jenkins/create_jobs.groovy. Verify which Forrest installation is still available and whether the Jenkins job definitions are current. Done means the publishing instructions and affected job configuration no longer depend on an unavailable installation.

Written by the indexing model from the issue text.