chore(docs): Add deep re-routing while switching between versions

[dishaprakash]

This PR alters the links of the version dropdown to make sure the links are deep routed while switching between versions

---

Should include a concise description of the changes (bug or feature), it's
impact, along with a summary of the solution

PR Checklist

---

Thank you for opening a Pull Request! Before submitting your PR, there are a
few things you can do to make sure it goes smoothly:

• Make sure you reviewed
  CONTRIBUTING.md
• Make sure to open an issue as a
  bug/issue
  before writing your code! That way we can discuss the change, evaluate
  designs, and agree on the general idea
• Ensure the tests and linter pass
• Code coverage does not decrease (if any source code was changed)
• Appropriate docs were updated (if necessary)
• Make sure to add ! if this involve a breaking change

🛠️ Fixes #<issue_number_goes_here>

[github-actions]

🔎 Preview at https://googleapis.github.io/genai-toolbox/previews/PR-1667/

[github-actions]

🔎 Preview at https://googleapis.github.io/genai-toolbox/previews/PR-1667/

[github-actions]

🔎 Preview at https://googleapis.github.io/genai-toolbox/previews/PR-1667/

[github-actions]

🔎 Preview at https://googleapis.github.io/genai-toolbox/previews/PR-1667/