Deprecate postgresql['data_dir']

• Add a deprecation message for 14.0
• Add documentation for using just postgresql['dir']

Test plan

• Without postgresql['data_dir'] set
  • Fresh install should not print out deprecation message
  • Upgrade should not print out deprecation message
• With postgresql['data_dir'] set
  • Fresh install should print out deprecation message
  • Upgrade should print out deprecation message

Closes #2214 (closed)