Improve dict-init-mutate msg suggestion

[clavedeluna]

Current problem

This PR added the dict-init-mutate check with a basic msg of Declare all known key/values when initializing the dictionary.. This issue is to improve that message to read something more like Declare all known key/values when initializing the dictionary with 'config = {'dir': 'bin', 'user': 'me', 'workers': 5}' which will require building the dictionary from nodes.

Desired solution

Use suggestion provided here https://github.com/PyCQA/pylint/pull/7794/files#r1027348441 to add code to DictInitMutateChecker to improve the msg suggestion.

Additional context

No response

[Pierre-Sassoulas]

An interesting test case:

        d = {"name": "table", "expectedrows": expectedrows}
        d["description"] = {a.cname: a.typ for a in self.axes}

Not sure of the message we should show when there is already some keys defined in the constructor.