[BE] Use default version of DB to create DB cluster

User story:

• When I going to create a DB cluster I need to have default versions selected so that I spend less time on version selection

UI/UX:
TBD

Acceptance criteria

• user see default version already selected on UI to use
• No additional action required from the user to use the default version

Out of scope:
N/A

Suggested implementation:

• Update API endpoints for DB cluster creation to include db version as optional field
• if DB version is empty
  • Use default DB version

• • • Check that DB version is supported by operator using version service
    • If it's not return an error? 
  • If default DB version isn't set yet use recommended DB version
• if DB version is set
  • Check that this DB version is supported by operators version
  • If this version is supported use this version
  • If this version is not supported by operator
• Implement for both endpoints

How to test:
TBD

Details:
TBD