in_tail: add option to skip permission errors during path scanning

[sandy2008]

Is your feature request related to a problem? Please describe.
When in_tail scans paths that include unreadable directories, it aborts on permission errors. In shared or hardened environments, this prevents tailing otherwise readable files.

Describe the solution you'd like
Add a configuration option (e.g., skip_permission_errors) that, when enabled, treats permission errors as non-fatal: log a warning, skip unreadable directories, and continue tailing readable files. Default should remain strict (fail on permission errors).

Describe alternatives you've considered

• Restricting glob patterns to only readable paths, which is brittle and hard to maintain.
• Running Fluent Bit with elevated permissions, which is not acceptable in many environments.
• Pre-filtering paths outside Fluent Bit, which adds operational complexity.

Additional context
This would allow in_tail to run reliably on nodes with mixed permissions while preserving the current strict behavior by default. And also we already have an PR: #10690