Add support for more field types

[zhongkairen]

To do

• [x] Text
• [x] Single selection - Priority
• [x] Number

[zhongkairen]

Numbers are synced as float, the format depends on the Airtable side, which doesn't support dynamic number format, i.e. fixed decimal places.

Single Selection - no option mapping currently supported, the options have to be added on Airtable side, and the texts need to be consistent with the ones in GitHub issues.

Iteration currently not supported. Airtable type should be single select or simply text.