feat(frontend): complete a subscription (#1942)

* feat(frontend): complete a subscription

Motivation
----------
Who: Users
What: Click on a button "Complete a subscription" to send money on a monthly basis to the company running "DreamMall".
Why: Because I want to support the development of this wonderful piece of software as well as the hosting and administration of it.

-----------
1. Visit http://localhost:3000/cockpit
2. Click on "Upgrade to premium"
3. See instructions how to make a bank transfer

You can change the amount and it will update the QR code.

There is another refactoring which affects the cockpit as a whole:
I removed the `narrow` property which is unnecessary.

close #1030

frontend/.env.dist

@@ -15,3 +15,7 @@ PUBLIC_ENV__ENDPOINTS__WEBSOCKET_URI=ws://localhost:4000/subscriptions
 # META
 PUBLIC_ENV__META__BASE_URL="http://localhost:3000"
 PUBLIC_ENV__META__DEFAULT_AUTHOR="DreamMall Verlag GbR"
+
+PUBLIC_ENV__ACCOUNT_HOLDER=
+PUBLIC_ENV__IBAN=
+PUBLIC_ENV__BIC=

frontend/.env.production

@@ -15,3 +15,7 @@ PUBLIC_ENV__ENDPOINTS__WEBSOCKET_URI=wss://master.git.dreammall.earth/api/subscr
 # META
 PUBLIC_ENV__META__BASE_URL="https://app.master.git.dreammall.earth"
 PUBLIC_ENV__META__DEFAULT_AUTHOR="DreamMall Verlag GbR"
+
+PUBLIC_ENV__ACCOUNT_HOLDER=
+PUBLIC_ENV__IBAN=
+PUBLIC_ENV__BIC=