[MINOR][SQL][DOCS] Fix description of days width in datetime patterns
[MINOR][SQL][DOCS] Fix description of days width in datetime patterns

### What changes were proposed in this pull request?
In the PR, I propose to fix the width of the day-of-month field to the maximum value 2:
<img width="573" alt="Screenshot 2022-07-21 at 21 11 11" src="https://user-images.githubusercontent.com/1580697/180284361-ac0d11f2-5fb2-4fa9-b950-8d5cf5e7b16f.png">

and clarify the behavior of parsing numbers:

<img width="751" alt="Screenshot 2022-07-21 at 21 11 23" src="https://user-images.githubusercontent.com/1580697/180284644-7af789af-5ebb-4e7e-a041-a00dea8c7b5b.png">

### Why are the changes needed?
To not confuse users and improve user experience with Spark SQL.

### Does this PR introduce _any_ user-facing change?
No.

### How was this patch tested?
By building docs and manually checking the changes.

Closes #37246 from MaxGekk/docs-fix-width-of-days.

Authored-by: Max Gekk <b91a34c712a29cd91cde3972985e114f1bb54d88@gmail.com>
Signed-off-by: Hyukjin Kwon <2680965ad5aae29275c8fb10150cb10f5554e78b@apache.org>

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