[chore/bugfix] Serve + throttle publickey separately from rest of ActivityPub API (#1461)

* serve publickey separately from AP, don't throttle it

* update nginx cache documentation, cache main-key too

* throttle public key, but separately from other endpoints

internal/api/activitypub/publickey/publickey.go

@@ -0,0 +1,48 @@
+/*
+   GoToSocial
+   Copyright (C) 2021-2023 GoToSocial Authors admin@gotosocial.org
+
+   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/>.
+*/
+
+package publickey
+
+import (
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+	"github.com/superseriousbusiness/gotosocial/internal/processing"
+	"github.com/superseriousbusiness/gotosocial/internal/uris"
+)
+
+const (
+	// UsernameKey is for account usernames.
+	UsernameKey = "username"
+	// PublicKeyPath is a path to a user's public key, for serving bare minimum AP representations.
+	PublicKeyPath = "users/:" + UsernameKey + "/" + uris.PublicKeyPath
+)
+
+type Module struct {
+	processor processing.Processor
+}
+
+func New(processor processing.Processor) *Module {
+	return &Module{
+		processor: processor,
+	}
+}
+
+func (m *Module) Route(attachHandler func(method string, path string, f ...gin.HandlerFunc) gin.IRoutes) {
+	attachHandler(http.MethodGet, "", m.PublicKeyGETHandler)
+}