Update event filters documentation

[joachimmetz]

in https://plaso.readthedocs.io/en/latest/sources/user/Event-filters.html

• Document use of PATH value type helpers - https://github.com/log2timeline/plaso/pull/4141
• using contains on lists
• rename pathspec to path_spec (double check if mapping is done for backwards compatibility)

[joachimmetz]

Extend PATH() helper to support globs and path segment separator