feat: add screenshot capture to measure charts

[AdityaHegde]

Uses html-to-image to take a screenshot of charts.

• Open a dialog with preview of what the screenshot will be. Based on mocks: https://linear.app/rilldata/issue/ENG-1099/download-explore-chart-as-png-with-left-side-data-callout#clickable-mock-b5824f7d
• Add a button to create the screenshot. For this this renders the image below the preview for quick testing, will be a download in the future.
• Make the button download the screenshot with <measure>_<from-time>_<to-time>.png file name.
• Match every elements of the mocks like add measure name, time range, comparison time range and filters.
• Make sure custom themes are applied correctly.

Popup with preview,

Downloaded screenshots,

Closes ENG-1099

Checklist:

• Covered by tests
• Ran it and it works as intended
• Reviewed the diff before requesting a review
• Checked for unhandled edge cases
• Linked the issues it closes
• Checked if the docs need to be updated. If so, create a separate Linear DOCS issue
• Intend to cherry-pick into the release branch
• I'm proud of this work!