(bugfix) Refactor property type in DateFilter for filtering on created_time and last_edited_time + fix documentation

[samzzi]

Current situation

• Documentation uses static constant which will not work: https://x.gnx.li/s61hn2G2
• If you use it correctly the call fails because the date type may not be used when using the 2 fixed timestamps (https://developers.notion.com/reference/post-database-query-filter#timestamp)

Proposed solution

• Check if property is timestamp and use proprtyname as type when it is

[mariosimao]

Released v1.12.0.