* feat: manage extensions navbar
create now `Manage` spacer in sidebar. and add manage extensions to it
closes#2088
* do not show when no exts
* update cn and jp i18n strings
* rename lnbits-admin-ui component to lnbits-manage, fix its behaviour
* i18n: add Korean language
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Co-authored-by: Pavol Rusnak <pavol@rusnak.io>
Co-authored-by: psychoet <125599543+psychoet@users.noreply.github.com>
