storage: start db migration (badger(hold))

migrating to badger, with the badgerhold frontend. So far, done:
* Announcements (small, for a quick test)
* Discord/Telegram/Matrix/Email

most interaction with badgerhold is done through the standard
Get<x>/Get<x>Key/Set<x>Key/Delete<x>Key. UserExists functions have been
added for email and matrix, and those and the original ones now use a
query against the database rather than sifting through every record.
I've tagged these searched fields as "index" for badgerhold, although this
definitely isn't used yet, and i'm not entirely sure if it'll be useful.

migrateToBadger is now in migrations.go, and a temporary config key
"migrated_to_badger" has been added, although it isn't being used yet,
migration is just running every time during development.

email.go

@@ -19,8 +19,10 @@ import (
 
 	"github.com/gomarkdown/markdown"
 	"github.com/gomarkdown/markdown/html"
+	"github.com/hrfee/mediabrowser"
 	"github.com/itchyny/timefmt-go"
 	"github.com/mailgun/mailgun-go/v4"
+	"github.com/timshannon/badgerhold/v4"
 	sMail "github.com/xhit/go-simple-mail/v2"
 )
 
@@ -874,31 +876,63 @@ func (app *appContext) getAddressOrName(jfID string) string {
 
 // ReverseUserSearch returns the jellyfin ID of the user with the given username, email, or contact method username.
 // returns "" if none found. returns only the first match, might be an issue if there are users with the same contact method usernames.
-func (app *appContext) ReverseUserSearch(address string) string {
+func (app *appContext) ReverseUserSearch(address string) (user mediabrowser.User, ok bool) {
+	ok = false
 	user, status, err := app.jf.UserByName(address, false)
 	if status == 200 && err == nil {
-		return user.ID
+		ok = true
+		return
 	}
-	for id, email := range app.storage.GetEmails() {
-		if strings.ToLower(address) == strings.ToLower(email.Addr) {
-			return id
+	emailAddresses := []EmailAddress{}
+	err = app.storage.db.Find(&emailAddresses, badgerhold.Where("Addr").Eq(address))
+	if err == nil && len(emailAddresses) > 0 {
+		for _, emailUser := range emailAddresses {
+			user, status, err = app.jf.UserByID(emailUser.JellyfinID, false)
+			if status == 200 && err == nil {
+				ok = true
+				return
+			}
 		}
 	}
-	for id, dcUser := range app.storage.GetDiscord() {
+	// Dont know how we'd use badgerhold when we need to render each username,
+	// Apart from storing the rendered name in the db.
+	for _, dcUser := range app.storage.GetDiscord() {
 		if RenderDiscordUsername(dcUser) == strings.ToLower(address) {
-			return id
+			user, status, err = app.jf.UserByID(dcUser.JellyfinID, false)
+			if status == 200 && err == nil {
+				ok = true
+				return
+			}
 		}
 	}
 	tgUsername := strings.TrimPrefix(address, "@")
-	for id, tgUser := range app.storage.GetTelegram() {
-		if tgUsername == tgUser.Username {
-			return id
+	telegramUsers := []TelegramUser{}
+	err = app.storage.db.Find(&telegramUsers, badgerhold.Where("Username").Eq(tgUsername))
+	if err == nil && len(telegramUsers) > 0 {
+		for _, telegramUser := range telegramUsers {
+			user, status, err = app.jf.UserByID(telegramUser.JellyfinID, false)
+			if status == 200 && err == nil {
+				ok = true
+				return
+			}
 		}
 	}
-	for id, mxUser := range app.storage.GetMatrix() {
-		if address == mxUser.UserID {
-			return id
+	matrixUsers := []MatrixUser{}
+	err = app.storage.db.Find(&matrixUsers, badgerhold.Where("UserID").Eq(address))
+	if err == nil && len(matrixUsers) > 0 {
+		for _, matrixUser := range matrixUsers {
+			user, status, err = app.jf.UserByID(matrixUser.JellyfinID, false)
+			if status == 200 && err == nil {
+				ok = true
+				return
+			}
 		}
 	}
-	return ""
+	return
+}
+
+// EmailAddressExists returns whether or not a user with the given email address exists.
+func (app *appContext) EmailAddressExists(address string) bool {
+	c, err := app.storage.db.Count(&EmailAddress{}, badgerhold.Where("Addr").Eq(address))
+	return err != nil || c > 0
 }