dev: use WooGraphQL 0.18.2 for LoginPayload fields

[kidunot89]

What

This PR defers the registration of LoginPayload.customer to WooGraphQL in v0.18.2+ (tba) which has added explicit support for this plugin.
Similarly, LoginPayload.wooSessionToken has been deprecated in favor of the sessionToken that WooGraphQL creates (and adds in v0.18.2+)

Why

Ecosystem interoperability.

How

Testing Instructions

Additional Info

Checklist:

• My code is tested to the best of my abilities.
• My code follows the WordPress Coding Standards.
• My code has proper inline documentation.
• I have added unit tests to verify the code works as intended.
• I included the relevant changes in CHANGELOG.md

[justlevine]

@kidunot89 if I understood the intent of this PR, it's to allow WooGraphQL to handle the registration of the customer and sessionToken fields.

However, it doesn't look like it's working with the latest WooGraphQL.

I believe this is because WooGraphQL only adds the fields to LoginPayload if WPGraphQL JWT Authentication exists.

[coveralls]

coverage: 82.646% (-0.2%) from 82.826% when pulling 1911066 on kidunot89:fix/woographql-conflicts-fix into 6a7e6c8 on AxeWP:develop.

[justlevine]

@kidunot89 I've updated the code to be backwards compatible with WooGraphQL < 0.18.2, as discussed.

I'm ready to merge unless you have any additional feedback.