Dashboard: Fix A11y in AutoRefresh input field

[joannaWebDev]

What is this feature?

This PR addresses the A11y concern of the AutoRefresh input inside the dashboard feature not specifying the clear format of the data the user needs to insert.

Why do we need this feature?

Relevant WCAG Criteria: [#.#.# WCAG Criterion](link to https://www.w3.org/WAI/WCAG21/quickref/?versions=2.0)
3.3.2 Labels or Instructions: https://www.w3.org/TR/WCAG21/#labels-or-instructions

Which issue(s) does this PR fix?:

Usage:

• "Fixes #A11y: Some input fields do not provide instructions for data formats above, below or before of the input field #82192"
• "Closes A11y: Some input fields do not provide instructions for data formats above, below or before of the input field #82192"

UI changes

Before	After

Special notes for your reviewer:

Please check that:

• It works as expected from a user's perspective.
• If this is a pre-GA feature, it is behind a feature toggle.
• The docs are updated, and if this is a notable improvement, it's added to our What's New doc.

[CLAassistant]

All committers have signed the CLA.

[ivanortegaalba]

Hi @joannaWebDev, thank you so much for contributing to Grafana!

From the engineering side, it looks good! Let me ask my colleagues from UX and docs to see if they are happy with the copies and we can merge it :)

@Ijin08 @imatwawana

[imatwawana]

Looks good to me!

[linoman]

@joannaWebDev Thank you so much for your contribution to Grafana!