Fixes #25225: Improve SVG image handling in the repo

[amousset]

https://issues.rudder.io/issues/25225

This PR introduces a difference between:

• Source files, for edition
  • All are current sources are SVG files, to be edited with Inkscape.
• Production files, derived automatically from the sources
  • Optimized SVG (size reduced by 40-90%)
  • Optimized bitmap (PNG/ICO)

Sources:

• Move all our SVG sources at the same place (webapp/sources/rudder/rudder-web/src/main/svg)
  • Remove duplicate existing logos
  • Contains logo sources from /logo and all SVG sources from the webapp
• Add a new notext source logo (required for the favicon)

Build:

• Build optimized SVG at webapp build time using gulp
• Add a script to rebuild the favicon from sources, but don't use it at build time (too many dependencies and the logo does not change often)
• Add a prebuilt set of optimized SVG files for external usage in /logo

Additionally:

• Remove an unused (ugly) background JPEG and the matching unused CSS rule.
• Remove the shortcut in the rel attribute of a link which should not be used:

Note: The shortcut link type is often seen before icon, but this link type is non-conforming, ignored and web authors must not use it anymore. (https://developer.mozilla.org/en-US/docs/Web/HTML/Attributes/rel#icon)

[amousset]

PR updated with a new commit

[amousset]

PR updated with a new commit

[amousset]

PR updated with a new commit