feature request: add label for paid endpoints to make it easier to understand which are free

[jcstein]

On https://api-docs.celenium.io/ it is difficult to tell which methods are free and which are paid. This feature would add some kind of label to the method that shows it is paid or free.

But...while writing this issue I realize that the paid endpoints show an "API key required", so maybe a link to the plans would do the trick here.

Free:

Paid:

[jcstein]

So I'm thinking:

"Example apiKey: 482402vjf2340rvsj029432jrs002 Get your API key."