### What changes were proposed in this pull request?
This PR proposes fix the default value in Data Source Option page based on the Scala documentation.
### Why are the changes needed?
Some of the existing default value in Data Source Option page follow the Python documentation, which has `None` as the default value for all options.
### Does this PR introduce _any_ user-facing change?
Yes, the default value in the Data Source Option page is fixed (from `None` to proper default value)
- Before
<img width="361" alt="Screen Shot 2021-06-02 at 6 31 12 PM" src="https://user-images.githubusercontent.com/44108233/120456594-b8719f00-c3d0-11eb-9778-071ab2ba9f45.png">
- After
<img width="562" alt="Screen Shot 2021-06-02 at 6 32 47 PM" src="https://user-images.githubusercontent.com/44108233/120456844-f1117880-c3d0-11eb-9c7c-9dcd66776444.png">
### How was this patch tested?
Manually built the docs and checked one by one.
Closes#32745 from itholic/SPARK-35523.
Lead-authored-by: itholic <haejoon.lee@databricks.com>
Co-authored-by: Haejoon Lee <44108233+itholic@users.noreply.github.com>
Signed-off-by: Hyukjin Kwon <gurwls223@apache.org>
### 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>
