[System]: Document values for filesystem.ignore_types

### Integration Name

System [packages/system]

### Dataset Name

system.filesystem

### Integration Version

1.58.2

### Agent Version

Any

### OS Version and Architecture

Any

### User Goal

Document the behavior of `List of filesystems to ignore` following https://github.com/elastic/integrations/issues/7703

We should improve the documentation associated to the, in particular:

- Set the List of filesystems to ignore empty => Defaults to Metricbeat behavior (nodev in `/proc/filesystems`)
- Set the List of filesystems to ignore to a list of valid filesystems to ignore => It will collect all of them except the ones specified
- Set the List of filesystems to ignore to a single space => It will render as `filesystem.ignore_types: []` which means do not ignore any filesystem

### Existing Features

The fix brought in https://github.com/elastic/integrations/issues/7703 helps

### What did you see?

The behavior is unclear now.

### Anything else?

_No response_