[MM-53968] Includes mattermost-plugin-api into the mono repo (#24235)

Include https://github.com/mattermost/mattermost-plugin-api into the mono repo

Co-authored-by: Jesse Hallam <jesse.hallam@gmail.com>
Co-authored-by: Michael Kochell <mjkochell@gmail.com>
Co-authored-by: Alejandro García Montoro <alejandro.garciamontoro@gmail.com>
Co-authored-by: Ben Schumacher <ben.schumacher@mattermost.com>
Co-authored-by: Alex Dovenmuehle <alex.dovenmuehle@mattermost.com>
Co-authored-by: Michael Kochell <6913320+mickmister@users.noreply.github.com>
Co-authored-by: Christopher Poile <cpoile@gmail.com>
Co-authored-by: İlker Göktuğ Öztürk <ilkergoktugozturk@gmail.com>
Co-authored-by: Shota Gvinepadze <wineson@gmail.com>
Co-authored-by: Ali Farooq <ali.farooq0@pm.me>
Co-authored-by: Maria A Nunez <maria.nunez@mattermost.com>
Co-authored-by: Daniel Espino García <larkox@gmail.com>
Co-authored-by: Christopher Speller <crspeller@gmail.com>
Co-authored-by: Alex Dovenmuehle <adovenmuehle@gmail.com>
Co-authored-by: Szymon Gibała <szymongib@gmail.com>
Co-authored-by: Lev <1187448+levb@users.noreply.github.com>
Co-authored-by: Jason Frerich <jason.frerich@mattermost.com>
Co-authored-by: Agniva De Sarker <agnivade@yahoo.co.in>
Co-authored-by: Artur M. Wolff <artur.m.wolff@gmail.com>
Co-authored-by: Madhav Hugar <16546715+madhavhugar@users.noreply.github.com>
Co-authored-by: Joe <security.joe@pm.me>
Co-authored-by: Ibrahim Serdar Acikgoz <serdaracikgoz86@gmail.com>
Co-authored-by: José Peso <trilopin@users.noreply.github.com>

server/public/pluginapi/emoji.go

@@ -0,0 +1,54 @@
+package pluginapi
+
+import (
+	"bytes"
+	"io"
+
+	"github.com/mattermost/mattermost/server/public/model"
+	"github.com/mattermost/mattermost/server/public/plugin"
+)
+
+// EmojiService exposes methods to manipulate emojis.
+type EmojiService struct {
+	api plugin.API
+}
+
+// Get gets a custom emoji by id.
+//
+// Minimum server version: 5.6
+func (e *EmojiService) Get(id string) (*model.Emoji, error) {
+	emoji, appErr := e.api.GetEmoji(id)
+
+	return emoji, normalizeAppErr(appErr)
+}
+
+// GetByName gets a custom emoji by its name.
+//
+// Minimum server version: 5.6
+func (e *EmojiService) GetByName(name string) (*model.Emoji, error) {
+	emoji, appErr := e.api.GetEmojiByName(name)
+
+	return emoji, normalizeAppErr(appErr)
+}
+
+// GetImage gets a custom emoji's content and format by id.
+//
+// Minimum server version: 5.6
+func (e *EmojiService) GetImage(id string) (io.Reader, string, error) {
+	contentBytes, format, appErr := e.api.GetEmojiImage(id)
+	if appErr != nil {
+		return nil, "", normalizeAppErr(appErr)
+	}
+
+	return bytes.NewReader(contentBytes), format, nil
+}
+
+// List retrieves a list of custom emojis.
+// sortBy parameter can be: "name".
+//
+// Minimum server version: 5.6
+func (e *EmojiService) List(sortBy string, page, count int) ([]*model.Emoji, error) {
+	emojis, appErr := e.api.GetEmojiList(sortBy, page, count)
+
+	return emojis, normalizeAppErr(appErr)
+}