service: Simple read only mode

[DanCodedThis]

• Ready only mode is a cli or env option
• Both exist in local and lambda mode
• Just checks env flag on execute
• Only allows:
  • Select (should allow union)
  • Use
  • Should allow With (cte)
  • Explain should work only on the statements above
• Added a service read only mode test
• Manual testing:
  • Local
  • Lambda

[DanCodedThis]

@rampage644 @osipovartem @Vedin

• Should we allow transaction statements (commit, rollback) that are not doing anything in read only mode?
• Or any statements which we support but not produce anything?
• Basically, what other statements should we have?