[fixbug] fix string type data parsing problem

[zhangshenghang]

What's changed?

https://github.com/apache/hertzbeat/issues/2050 https://github.com/apache/hertzbeat/issues/1873 https://github.com/apache/hertzbeat/pull/1884

• Modify the data whose field type is equal to CommonConstants.TYPE_STRING, and do not execute the extractDoubleAndUnitFromStr method
• Optimize the judgment logic

Verified monitoring modules

I have verified the contents of the following monitoring and preliminarily confirmed that the modification is fine, but I need help to confirm whether my verification is comprehensive. @tomsun28

Checklist

• [x] I have read the Contributing Guide
• [x] I have written the necessary doc or comment.

[zhangshenghang]

@tomsun28 Fix completed