Ease assertions on content of JSON files

[fstaudt]

Is your feature request related to a problem? Please describe.
There is no simple way provided by json-unit-assertj module to assert JSON directly from a JSON file.
It is always required to read the file content before we can use assertThatJson.

Describe the solution you'd like
Logic to parse a JSON file should be encapsulated in a new class (e.g. JsonFileAssert).

This class should only read the file and delegate JSON assertions on file content to ConfigurableJsonAssert (e.g. hasContent()):

assertThatJsonFile(File("file.json")).hasContent().node("key").isEqualTo("value");

Describe alternatives you've considered
N/A

Additional context
I can provide a PR for this change

[lukas-krecan]

Hi, sorry for the late response. I do not think this belongs to the library. It's straigtforward to implement on your side and it would bloat the API unnecesarilly.