Support additional URL attribute prefixes

[xuangeyouneihan]

Summary

Not all KeePass clients store additional URLs to KP2A_URL*, so we need an option to scan attributes whose value is a URL and use them as additional URLs as well.

Examples

For example, KeePassDX stores additional URLs to URL_* (e. g. URL_1), and StrongBox's document recommends users to manually store additional URLs to URL* (e. g. URL2).

Context

For instance, I use KeePassXC on my PC, KeePassDX on my Android Phone, and Strongbox (or FantasyPass) on my iPad. Only KeePassXC does not scan URLs in all attributes.