Add Tooltip for Vote Context Field with Link to GitHub Storage Guide

## Description
Add a **tooltip button** in addition to the vote context (rationale) when users are adding or updating their vote on a governance action.
The tooltip should contain a brief explanation and link to **documentation** that explains **how to store files on GitHub**, intended to help users understand how to host and reference rationale metadata.

Additionally, there's an **open question** to address:
> Do we or should we validate vote context/rationale metadata?

## Acceptance Criteria
- [ ] A **tooltip button** is added next to the vote context input field.
- [ ] Tooltip contains helpful text and a link to the documentation on **how to store files on GitHub**.
- [ ] Tooltip is accessible and behaves consistently across browsers.
- [ ] The open question about **vote rationale metadata validation** is acknowledged and tracked for discussion or future implementation.