Update `export` command to be flexible with HTTP/HTTPS ports

Currently, export command uses https endpoint but if it fails it will use http endpoint. but considering it's security implications we would like to add a cli option in the `export` command which will specify if we need to allow the use of fallback http url or not.

Add a cli option in `export` command.

Suggested Option:
`--allow-http-fallback`
Type: Boolean
Default Value: false
value required: No (acts like a switch)

example:
`dab export --graphql -o ./schema --allow-http-fallback`