* Add tenant.AllowedSchemes advanced configuration item

Specifying ^monero:[48] or ^bitcoin:(1|3|bc1) allows cryptocurrency
payment links

These were rendered but then sanitised away to <a>...</a> w/o href=

Ref: https://bounties.monero.social/posts/15/1-200m-monero-bounties-site-parse-donation-address-as-link

* Ship the config via useFider()

* Work around useContext() restrixion in test

* Disable allowed schemes by setting ALLOW_ALLOWED_SCHEMES=false

* Hide Allowed URL Schemes config if disabled

* Bump migration date