Return the PNID's Stripe tier name and level from the PNID details API

[MatthewL246]

This is a necessary for PretendoNetwork/website#345

Changes:

This modifies the GET https://api.pretendo.cc/v1/user API to return the PNID's Stripe tier name and level. This is necessary for Discourse group syncing because the Discourse SSO route on the website calls this API to retreive account details, and the tier name/level will be needed to sync the supporter groups.

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[binaryoverload]

I don't know what the types are here, but I reckon connections, and stripe can be undefined, which would cause an error.

I would suggest either:
a) use a ternary to say stripe: pnid.connections?.stripe ? { ... } : null
b) use optional chaining on the properties, i.e pnid.connections?.stripe?.tier_name

Option a) would give the stripe object the possibility to be null, and option b) would ensure the object would always be present but with possibly null values.