HDDS-4647. Avoid hadoop-ozone-filesystem-shaded as transitive dependency

[adoroszlai]

What changes were proposed in this pull request?

If hadoop-ozone-filesystem-hadoop2 or hadoop-ozone-filesystem-hadoop3 is added as dependency in some project, hadoop-ozone-filesystem-shaded is included as a transitive dependency. But it should not be required for such downstream projects, as both Hadoop version-specific modules already repackage most of it. This change marks the dependency as optional (doc) so that such projects do not need to add exclusion for this module.

https://issues.apache.org/jira/browse/HDDS-4647

How was this patch tested?

Checked dependency tree of downstream project no longer includes hadoop-ozone-filesystem-shaded:

[INFO] --- maven-dependency-plugin:2.8:tree (default-cli) @ tez ---
[INFO] ...
[INFO] +- jdk.tools:jdk.tools:jar:1.8:system
[INFO] \- org.apache.hadoop:hadoop-ozone-filesystem-hadoop3:jar:1.1.0-SNAPSHOT:runtime
[INFO] ------------------------------------------------------------------------

Regular CI:
https://github.com/adoroszlai/hadoop-ozone/actions/runs/465890389

[elek]

+1 thanks the fix @adoroszlai

Pending on CI

[adoroszlai]

Thanks @elek and @mukul1987 for the review.