### What changes were proposed in this pull request?
This PR aims to add a documentation on how to read and write TEXT files through various APIs such as Scala, Python and JAVA in Spark to [Data Source documents](https://spark.apache.org/docs/latest/sql-data-sources.html#data-sources).
### Why are the changes needed?
Documentation on how Spark handles TEXT files is missing. It should be added to the document for user convenience.
### Does this PR introduce _any_ user-facing change?
Yes, this PR adds a new page to Data Sources documents.
### How was this patch tested?
Manually build documents and check the page on local as below.
Closes#32053 from itholic/SPARK-34491-TEXT.
Authored-by: itholic <haejoon.lee@databricks.com>
Signed-off-by: Max Gekk <max.gekk@gmail.com>
