feat: add password reset for usermanager (#2688)

* feat: add password reset for usermanager
- add a reset_key to account table
- add ?reset_key= GET arguments to index.html and show reset form if provided
- superuser can generate and copy reset url with key to share
future ideas:
- could add send forgot password email if user fill out email address
* feat: simplify reset key
* test: use reset key
* test: add more tests
* test: reset passwords do not match
* test: `reset_password_auth_threshold_expired`

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Co-authored-by: Vlad Stan <stan.v.vlad@gmail.com>

lnbits/static/i18n/en.js

@@ -266,5 +266,7 @@ window.localisation.en = {
   hide_empty_wallets: 'Hide empty wallets',
   recheck: 'Recheck',
   contributors: 'Contributors',
-  license: 'License'
+  license: 'License',
+  reset_key: 'Reset Key',
+  reset_password: 'Reset Password'
 }