Add browserless support

[SnowyLeopard]

Topic and Scope

Inspired by https://github.com/nextcloud/cookbook/pull/2622 this adds support for the use of browserless(.io). This allows fetching recipes from websites that need javascript to be executed and bypasses bot detection for some websites.

Concerns/issues

• I haven't figured out yet how to store the token securely, now it is just saved as plain text in the DB.
• Does this need more readme/how to documentation?

Formal requirements

There are some formal requirements that should be satisfied. Please mark those by checking the corresponding box.

• [x] I did check that the app can still be opened and does not throw any browser logs
• [x] I created tests for newly added PHP code (check this if no PHP changes were made)
• [x] I updated the OpenAPI specs and added an entry to the API changelog (check if API was not modified)
• [ ] I notified the matrix channel if I introduced an API change