Add DPG badge to the homepage and the README

[Xpirix]

Fix for #547

• Added the DPG badge next to the Free and Open Source label
• Clicking on the badge will open the blog post (https://blog.qgis.org/2025/02/08/qgis-recognized-as-digital-public-good/) in a new tab
• Show the DPG badge on this repository's README

[anitagraser]

The Readme badge is good. I'm OK with that.

The badge on the home page needs some more work:

1. It's now visually more prominent than the "open source" badge, but that does not reflect the true importance. The visual impact of DPG should be <= open source.
2. On a related note: the outline of the DPG batch should be the same width (or thinner) than the open source badge's outline.
3. The DPG badge's blue shades does not match any of our colors. This makes it look very jarring. Can we have a b/w version?
4. Finally, my OCD is triggered by the outline "cutting off" the white circle on the left: It just doesn't feel aligned correctly.

[anitagraser]

This image needs some padding on the left, so that the circle on the left is properly displayed

[Xpirix]

Thank you very much for the review @anitagraser.

• I've updated it using the white version and reviewed the design.
• I've also decreased the opacity to 80% to make it less attractive.
• The left padding of the image has been adjusted to make the circle appear correctly
• The outline has been adjusted to match the width of the Free and Open Source label

What do you think about this?

Here is a zoomed-in version:

[anitagraser]

Much better, thanks. Maybe 70% opacity for the image to match the outline more closely.

[Xpirix]

The outline and the badge opacity are now aligned

[anitagraser]

Perfect. Good to merge for me