Add SVG format option for favicon image

[aduth]

🛠 Summary of changes

Adds a new SVG image format option to the set of existing favicon images.

Why?

• Infinitely scalable
• Smaller file size
• With future browser support, simpler to implement vs. several size options (see current browser support)

The process for creating this was starting from login-gov-logo.svg, cropping to the badge shield (landed at 34x42 padded to 48x48), experimenting with padding options in-context, then minifying.

📜 Testing Plan

I tested this in identity-idp and compared against the live https://secure.login.gov

diff --git a/app/assets/images/favicons/favicon.svg b/app/assets/images/favicons/favicon.svg
new file mode 100644
index 0000000000..0ca5346abd
--- /dev/null
+++ b/app/assets/images/favicons/favicon.svg
@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 48 48"><path fill="#b51e23" d="M35.905 3h-11.91v42c11.3-5 15.25-11.48 16.25-13.5.187-.387.283-.811.28-1.24V7.62A4.62 4.62 0 0 0 35.905 3z"/><path fill="#e21d3e" d="M12.095 3a4.62 4.62 0 0 0-4.62 4.62v22.64a2.77 2.77 0 0 0 .28 1.24c1 2 5 8.53 16.24 13.5V3h-11.9z"/><path fill="#fff" d="M26.925 21.1c2.837-2.233 2.194-6.7-1.158-8.041s-6.899 1.45-6.384 5.023a4.69 4.69 0 0 0 1.742 3.018l-1.54 8.82c1.457.252 2.932.379 4.41.38 1.5.03 2.998-.07 4.48-.3l-1.55-8.9z"/></svg>
\ No newline at end of file
diff --git a/app/views/layouts/base.html.erb b/app/views/layouts/base.html.erb
index dfb2599f44..837d175790 100644
--- a/app/views/layouts/base.html.erb
+++ b/app/views/layouts/base.html.erb
@@ -46,2 +46,8 @@
       ) %>
+  <%= favicon_link_tag(
+        asset_path('favicons/favicon.svg'),
+        rel: 'icon',
+        sizes: 'any',
+        type: 'image/svg+xml',
+      ) %>
   <%= favicon_link_tag(

👀 Screenshots

In context comparison (left is SVG, right is current PNG):

SVG (294 bytes Brotli)	PNG (413 bytes)