Update cli UX

Picodata follow-up

Updates in picdata admin and picodata connect CLI:

1. EOF is a delimiter for files
2. New inner_prompt for command that is incomplete (command is incomplete until delimiter is specified)
3. Special commands can be called without delimiter
4. New special command \set delimiter enter to change delimiter to EOL (end of line - enter)

See the screenshots in the comments

• Follow-up for picodata!1390 (merged)
• See also picodata#1059 (closed), picodata#1065 (closed), picodata#1067 (closed)
• Doc pages to change: everywhere