Add options for logo and favicon

[secondtruth]

Is your feature request related to a problem? Please describe.
Not directly related to a problem, but enhancing customization options could improve user experience and adaptability of SearXNG for different deployments.

Describe the solution you'd like
I propose adding an option in the settings to allow administrators to easily change the logo (and favicon) used in SearXNG's templates. This would enable a more personalized search engine experience and support branding for private deployments or community instances.

Describe alternatives you've considered
As an alternative, detailed documentation could be provided on how to manually change the logo by editing the template files or using container path binds, although this approach is less accessible for users with limited technical expertise.

Additional context

• Changing The Logo #2032