Allow micoseconds for datetime filters

[KhaledBousrih]

Currently, the datetime filters only accept these two formats:

• YYYY-MM-DD
• YYYY-MM-DDTHH:mm:ssZ

We should be able to also accept the format with the microseconds YYYY-MM-DDTHH:mm:ss.xxxxxxZ with at most 6 digits for microseconds (regex: r'^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}(\.\d{1,6})?Z$')