[feature] Admin accounts endpoints; approve/reject sign-ups (#2826)

* update settings panels, add pending overview + approve/deny functions

* add admin accounts get, approve, reject

* send approved/rejected emails

* use signup URL

* docs!

* email

* swagger

* web linting

* fix email tests

* wee lil fixerinos

* use new paging logic for GetAccounts() series of admin endpoints, small changes to query building

* shuffle useAccountIDIn check *before* adding to query

* fix parse from toot react error

* use `netip.Addr`

* put valid slices in globals

* optimistic updates for account state

---------

Co-authored-by: kim <grufwub@gmail.com>

web/template/email_signup_rejected.tmpl

@@ -0,0 +1,28 @@
+{{- /*
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/ -}}
+
+Hello!
+
+You are receiving this mail because your request for an account on {{ .InstanceName }} has been rejected by a moderator.
+
+{{ if .Message }}The moderator who handled the sign-up included the following message regarding this rejection: "{{- .Message -}}"{{ end }}
+
+---
+
+If you believe you've been sent this email in error, feel free to ignore it, or contact the administrator of {{ .InstanceURL -}}.