Removed no_snippets build option.

Instead, we now read a configuration file, zls.json in the same folder as the executable.
Options are defined in the struct config.zig and must have default values.
The only option right now is enable_snippets and it defaults to true.

build.zig

@@ -23,12 +23,6 @@ pub fn build(b: *std.build.Builder) !void {
         data_version,
     );
 
-    exe.addBuildOption(
-        bool,
-        "no_snippets",
-        b.option(bool, "no_snippets", "Use regular completion without snippets. Useful for compatibility.") orelse false,
-    );
-
     exe.addBuildOption(
         bool,
         "allocation_info",