Pass proper parameters to launch a login window

D89966-code introduces new parameters that we have to pass according to the post setting:
- source=jetpack_post_paid
- source=jetpack_subscribe
- source=jetpack_post_email_only

We want to pass an appropriate access level that we introduced in the https://github.com/Automattic/jetpack/pull/26417 .
- We probably need to change the specific names inside WPCOM codebase to match what we have in Jetpack
- We need to pass what we have in Jetpack to the proper parameter.