feat: support symlink file detect

[luohoufu]

What does this PR do

support symlink file detect and fix symlink file nil check

Rationale for this change

This pull request includes several enhancements and bug fixes in the lib/reader/harvester/harvester.go, lib/util/file.go, and plugin/logs/file_detect.go files. The changes focus on improving error handling, removing unused code, and adding new utility functions.

Error handling improvements:

• lib/reader/harvester/harvester.go: Added checks to ensure the file is not nil before proceeding with operations in the NewHarvester, NewJsonFileReader, and NewLogFileReader functions. [1] [2] [3] [4]

Code cleanup:

• lib/reader/harvester/harvester.go: Removed the unused NewPlainTextRead function.

New utility functions:

• lib/util/file.go: Added CountFileRows and ResolveSymlink functions to count the number of rows in a file and resolve the target file path of a symbolic link, respectively. [1] [2] [3]

Integration of new utility functions:

• plugin/logs/file_detect.go: Integrated the ResolveSymlink function to handle symbolic links in the judgeEvent method. [1] [2]

Standards checklist

• The PR title is descriptive
• The commit messages are semantic
• Necessary tests are added
• Updated the release notes
• Necessary documents have been added if this is a new feature
• Performance tests checked, no obvious performance degradation