API to directly return avatar image

[lightwalker-eth]

Goals include:

• Query by both name or address
• Optimize size(s)
• Protect against nasty .svg files or other edge cases
• Caching (with smart cache invalidations)
• Also support cover images (not just avatar images)

References to consider include:

• https://github.com/ensdomains/ens-metadata-service
• https://github.com/ensdomains/ens-avatar
• https://enstate.rs/docs#tag/avatars--banners
• https://ensdata.net/
• https://github.com/gskril/ens-api