[MINOR][DOCS] Fix spacings in Structured Streaming Programming Guide

## What changes were proposed in this pull request?

1. Omitted space between the sentences: `... on static data.The Spark SQL engine will ...` -> `... on static data. The Spark SQL engine will ...`
2. Omitted colon in Output Model section.

## How was this patch tested?

None.

Author: Lee Dongjin <dongjin@apache.org>

Closes #17564 from dongjinleekr/feature/fix-programming-guide.