[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/experimental/bot/poster/default_poster.go

@@ -0,0 +1,76 @@
+package poster
+
+import (
+	"fmt"
+
+	"github.com/mattermost/mattermost/server/public/model"
+)
+
+type defaultPoster struct {
+	postAPI PostAPI
+	id      string
+}
+
+// NewPoster creates a new default poster
+func NewPoster(postAPI PostAPI, id string) Poster {
+	return &defaultPoster{
+		postAPI: postAPI,
+		id:      id,
+	}
+}
+
+// DM posts a simple Direct Message to the specified user
+func (p *defaultPoster) DM(mattermostUserID, format string, args ...interface{}) (string, error) {
+	post := &model.Post{
+		Message: fmt.Sprintf(format, args...),
+	}
+	err := p.postAPI.DM(p.id, mattermostUserID, post)
+	if err != nil {
+		return "", err
+	}
+	return post.Id, nil
+}
+
+// DMWithAttachments posts a Direct Message that contains Slack attachments.
+// Often used to include post actions.
+func (p *defaultPoster) DMWithAttachments(mattermostUserID string, attachments ...*model.SlackAttachment) (string, error) {
+	post := model.Post{}
+	model.ParseSlackAttachment(&post, attachments)
+	err := p.postAPI.DM(p.id, mattermostUserID, &post)
+	if err != nil {
+		return "", err
+	}
+	return post.Id, nil
+}
+
+// Ephemeral sends an ephemeral message to a user
+func (p *defaultPoster) Ephemeral(userID, channelID, format string, args ...interface{}) {
+	post := &model.Post{
+		UserId:    p.id,
+		ChannelId: channelID,
+		Message:   fmt.Sprintf(format, args...),
+	}
+	p.postAPI.SendEphemeralPost(userID, post)
+}
+
+func (p *defaultPoster) UpdatePostByID(postID, format string, args ...interface{}) error {
+	post, err := p.postAPI.GetPost(postID)
+	if err != nil {
+		return err
+	}
+
+	post.Message = fmt.Sprintf(format, args...)
+	return p.UpdatePost(post)
+}
+
+func (p *defaultPoster) DeletePost(postID string) error {
+	return p.postAPI.DeletePost(postID)
+}
+
+func (p *defaultPoster) UpdatePost(post *model.Post) error {
+	return p.postAPI.UpdatePost(post)
+}
+
+func (p *defaultPoster) UpdatePosterID(id string) {
+	p.id = id
+}