Add KV helper methods to Helpers interface (#11307)

* Add KV helper methods to Helpers interface

* Address code-review comments, add unit tests

* Update documentation for KVCompareAndSetJSON.

* Update assertions for helpers_bots_test.go

* Fix assertion not called name in test.

plugin/helpers_bots.go

@@ -4,6 +4,7 @@
 package plugin
 
 import (
+	"encoding/json"
 	"time"
 
 	"github.com/mattermost/mattermost-server/model"
@@ -64,3 +65,42 @@ func (p *HelpersImpl) EnsureBot(bot *model.Bot) (retBotId string, retErr error)
 
 	return createdBot.UserId, nil
 }
+
+func (p *HelpersImpl) KVGetJSON(key string, value interface{}) error {
+	data, err := p.API.KVGet(key)
+	if err != nil {
+		return err
+	}
+
+	return json.Unmarshal(data, value)
+}
+
+func (p *HelpersImpl) KVSetJSON(key string, value interface{}) error {
+	data, err := json.Marshal(value)
+	if err != nil {
+		return err
+	}
+	return p.API.KVSet(key, data)
+}
+
+func (p *HelpersImpl) KVCompareAndSetJSON(key string, oldValue interface{}, newValue interface{}) (bool, error) {
+	oldData, err := json.Marshal(oldValue)
+	if err != nil {
+		return false, errors.Wrap(err, "unable to marshal old value")
+	}
+
+	newData, err := json.Marshal(newValue)
+	if err != nil {
+		return false, errors.Wrap(err, "unable to marshal new value")
+	}
+
+	return p.API.KVCompareAndSet(key, oldData, newData)
+}
+
+func (p *HelpersImpl) KVSetWithExpiryJSON(key string, value interface{}, expireInSeconds int64) error {
+	data, err := json.Marshal(value)
+	if err != nil {
+		return err
+	}
+	return p.API.KVSetWithExpiry(key, data, expireInSeconds)
+}