[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>
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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>
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Co-authored-by: Jason Frerich <jason.frerich@mattermost.com>
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server/public/pluginapi/cluster/mutex_example_test.go

@@ -0,0 +1,20 @@
+package cluster_test
+
+import (
+	"github.com/mattermost/mattermost/server/public/plugin"
+	"github.com/mattermost/mattermost/server/public/pluginapi/cluster"
+)
+
+//nolint:staticcheck
+func ExampleMutex() {
+	// Use p.API from your plugin instead.
+	pluginAPI := plugin.API(nil)
+
+	m, err := cluster.NewMutex(pluginAPI, "key")
+	if err != nil {
+		panic(err)
+	}
+	m.Lock()
+	// critical section
+	m.Unlock()
+}