[FEATURE]Add `datefloor` PPL command

[YANG-DB]

Is your feature request related to a problem?
Add datefloor command for PPL spark based execution driver .

Since spark sql doesnt offer such expression a possible option would be:

• use date_truncate spark sql command
• register a custom expression datefloor

Do you have any additional context?

• [META]Add Missing PPL commands - campaign #408