[FR]: Allow vale to work with multiple file tyes

### What is the current behavior?

Currently, the vale linter in this package only supports linting Markdown files.

### Describe the feature

Vale itself supports linting a wide range of filetypes. That should be enabled here.

The issue names no files, tests, or entry points; start by locating the Vale linter rule in this Bazel-based package and finding where Markdown-only support is enforced. Done means the rule can lint Vale-supported file types beyond Markdown, with coverage for the supported behavior.

Written by the indexing model from the issue text.