Dev: enforce consistent styles with EditorConfig (#34)

CLOSE
https://linear.app/sourcegraph/issue/CODY-3142/set-up-linter-formatter

Thanks to Piotr for letting us know about the EditorConfig file which
allows us to enforce consistent styles with EditorConfig to avoid
inconsistent spacing and formatting that would cause diff conflicts.

Please feel free to suggest any changes to the configurations before I
run them code clean up on all the files in the current codebase. Any
code that's added after the editorconfig file will be automatically
cleaned up:
https://learn.microsoft.com/en-us/visualstudio/ide/create-portable-custom-editor-options?view=vs-2022

See
https://learn.microsoft.com/en-us/visualstudio/ide/code-styles-and-code-cleanup?view=vs-2022&source=recommendations

src/.editorconfig

@@ -0,0 +1,33 @@
+# Remove the line below if you want to inherit .editorconfig settings from higher directories
+root = true
+
+# Matches Cody Main Repository
+[*]
+insert_final_newline = true
+end_of_line = lf
+charset = utf-8
+trim_trailing_whitespace = true
+indent_style = space
+indent_size = 4
+
+[{*.json,*.yml,*.yaml,*.md}]
+indent_size = 2
+
+[*.md]
+trim_trailing_whitespace = false
+
+[{*.sh, *.bash}]
+indent_style = space
+indent_size = 2
+switch_case_indent = true
+
+[**/{node_modules,dist}/**]
+ignore = true
+
+# C# files
+[*.cs]
+
+#### Core EditorConfig Options ####
+
+# Indentation and spacing
+tab_width = 4