lint: enable linter in docs and fix issues (#6400)

- Removed temporary ignores for the docs package.
- Updated linting rules for the docs package to improve code quality.
- Refactored variable declarations from `let` to `const` for better consistency.
- Added a new configuration file for oxlint in the docs directory.
- Made minor formatting adjustments across various components.

.oxlintrc.json

@@ -233,7 +233,6 @@
 
     {
       "files": [
-        "packages/docs/**/*", // TODO: fix these issues
         "packages/api/migrations/*",
         "packages/loot-core/migrations/*",
         "packages/sync-server/src/app-gocardless/banks/*.js",