Add Vale linter for TUF documentation

[Ayush9026]

Description of issue or feature request: Add Vale linter for TUF documentation

Current behavior: Currently, the TUF documentation does not utilize a linter to ensure consistency and quality in the writing style. This can lead to inconsistencies and potential readability issues across different documentation sections.

Expected behavior: Integrate Vale linter into the TUF documentation workflow to automatically check for style and grammar issues. This will ensure a consistent and high-quality documentation style. The Vale linter should be configured to use a set of rules that align with the TUF project's documentation standards.