Filter out diagnostics if they are in docsstring

[mzaks]

This PR allows suppression of warnings and errors in docstrings. Although this is generally useful to see warnings and errors in docstrings snippets in some cases, making a fully correct code in docstring snippets means clutter which obscures the example you want to highlight in the docstring. A good example is the mojo standard library, many files have warning and errors in docstrings, which introduces noise and does not help.

The PR introduces a config entry for suppression which defaults to false, so the default behavior is same as we have now.

Alternative consideration:

• we could also not fully suppress the diagnostics but set warning and errors in doctstring to information level.
• It would be great if we could send a flag to the language server to not emit the diagnostics for the docstrings, which would reduce compute on extension and language server side.