feat(lxlweb): Read site configuration from backend.

[olovy]

Read site configuration from backend.

configuration now can:

• override locale / translations
• select theme
  • the actual theme is still part of lxl-web
• select hero image
  • hero image is still part of lxl-web
  • added two new example hero images (a11y fail! do not work well text on them...)
• select favicon
  • favicon is still part of lxl-web
• disable some features
  • favourite libraries
  • my pages
  • holdings (i.e no "0 libraries")
  • special collections
  • disable resource images / placeholders completely. ege Swepub and Uppsök never have images (for now).
    • TODO: Doesn't look great. Fix layout when images disabled.
• set footer sections / links
• set featured searches
• override about page
• add additional app menu items
  • home / search / help / about / language are fixed for now

See libris/definitions#620 for Swepub / Uppsök example config
NB! hero images are just examples. TBD!

Libris default values for everything are still set in lxl-web.

Only SEARCH_SITE remains in .env. Used to fetch settings.
For now SUBSITES is only used to prefetch all settings. Maybe we don't need it?
Example .env

SUBSITES=suecia,swepub,uppsok
SUBSITE.suecia.SEARCH_SITE=https://suecia.kb.se/
SUBSITE.swepub.SEARCH_SITE=https://swepub.kb.se/
SUBSITE.uppsok.SEARCH_SITE=https://uppsok.libris.kb.se/

I recommend turning off whitespace in diff view for "feature flag" changes.

TODO

• featured categories
• featured / visible filters

[lrosenstrom]

LGTM! Also looked promising on the live demonstration. Let's revisit how we can utilize the hero image customizability later with some better background images.