[feature] implement custom_emojis endpoint (#563)

* implement custom_emojis api endpoint

* add tests for getting custom emoji out of the database and converting to api emoji

* change sort direction of emoji query

* change logging level and initialize array with known length as per kim's suggestions

* add continue to lessen risk of making a malformed struct during conversion from db to api emojis

internal/processing/media/getemoji_test.go

@@ -0,0 +1,42 @@
+/*
+   GoToSocial
+   Copyright (C) 2021-2022 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 media_test
+
+import (
+	"context"
+	"testing"
+
+	"github.com/stretchr/testify/suite"
+)
+
+type GetEmojiTestSuite struct {
+	MediaStandardTestSuite
+}
+
+func (suite *GetEmojiTestSuite) TestGetCustomEmojis() {
+	emojis, err := suite.mediaProcessor.GetCustomEmojis(context.Background())
+
+	suite.NoError(err)
+	suite.Equal(1, len(emojis))
+	suite.Equal("rainbow", emojis[0].Shortcode)
+}
+
+func TestGetEmojiTestSuite(t *testing.T) {
+	suite.Run(t, &GetEmojiTestSuite{})
+}