Add support for a lint configuration file

[davidanthoff]

Interesting prior art discussion at https://github.com/rust-lang/rfcs/blob/master/text/3389-manifest-lint.md.

[ufechner7]

Shall it be .yaml or .toml ?

Is there already a list of features that we might want to turn on or off?

[davidanthoff]

There is already a basic implementation for this in the code right now. Essentially it looks for files called .JuliaLint.toml, and then applies those settings to the folder it is in and all children.

Currently it supports these

JuliaWorkspaces.jl/src/layer_diagnostics.jl

Line 13 in dceae47

valid_lint_configs = ["syntax-errors", "syntax-warnings", "testitem-errors", "toml-syntax-errors", "lint-config-errors"]

config values, with a simple true or false.

There are really two things that we need to do here:

1. Add more config options, in particular configuration options for the legacy lint options that are in StaticLint.jl. As I move SymbolServer and StaticLint into JuliaWorkspaces, that is going to happen as part of that work.
2. Decide whether the config file format is good :) My gut feeling is that it is probably too simplistic... We might prefer something where there is a rule, and then one can decide whether that should result in an info/warning/error. And maybe also more config options... Just not sure yet.