[Doc] Improve documentation on usage of Schema metadata and usage/limitations in Execplan

Schema metadata can be an important aspect related to computation and maintaining states. How this is affected in the execution plan and how it needs to be handled can be further documented. 

**Reporter**: [Vibhatha Lakmal Abeykoon](https://issues.apache.org/jira/browse/ARROW-15543) / @vibhatha

_{**Note**: *This issue was originally created as [ARROW-15543](https://issues.apache.org/jira/browse/ARROW-15543). Please see the [migration documentation](https://github.com/apache/arrow/issues/14542) for further details.*}

Start with the issue's discussion of schema metadata and execution plans, then review the linked migration documentation for context. Done means the documentation explains how schema metadata affects execution plans, including its usage and limitations; the issue does not name a documentation file or test to run.

Written by the indexing model from the issue text.