PLT-8131 (part2) Add plugin key value store support (#7902)

* Add plugin key value store support

* Add localization strings

* Updates per feedback

store/storetest/mocks/PluginStore.go

@@ -0,0 +1,62 @@
+// Code generated by mockery v1.0.0
+
+// Regenerate this file using `make store-mocks`.
+
+package mocks
+
+import mock "github.com/stretchr/testify/mock"
+import model "github.com/mattermost/mattermost-server/model"
+import store "github.com/mattermost/mattermost-server/store"
+
+// PluginStore is an autogenerated mock type for the PluginStore type
+type PluginStore struct {
+	mock.Mock
+}
+
+// Delete provides a mock function with given fields: pluginId, key
+func (_m *PluginStore) Delete(pluginId string, key string) store.StoreChannel {
+	ret := _m.Called(pluginId, key)
+
+	var r0 store.StoreChannel
+	if rf, ok := ret.Get(0).(func(string, string) store.StoreChannel); ok {
+		r0 = rf(pluginId, key)
+	} else {
+		if ret.Get(0) != nil {
+			r0 = ret.Get(0).(store.StoreChannel)
+		}
+	}
+
+	return r0
+}
+
+// Get provides a mock function with given fields: pluginId, key
+func (_m *PluginStore) Get(pluginId string, key string) store.StoreChannel {
+	ret := _m.Called(pluginId, key)
+
+	var r0 store.StoreChannel
+	if rf, ok := ret.Get(0).(func(string, string) store.StoreChannel); ok {
+		r0 = rf(pluginId, key)
+	} else {
+		if ret.Get(0) != nil {
+			r0 = ret.Get(0).(store.StoreChannel)
+		}
+	}
+
+	return r0
+}
+
+// SaveOrUpdate provides a mock function with given fields: keyVal
+func (_m *PluginStore) SaveOrUpdate(keyVal *model.PluginKeyValue) store.StoreChannel {
+	ret := _m.Called(keyVal)
+
+	var r0 store.StoreChannel
+	if rf, ok := ret.Get(0).(func(*model.PluginKeyValue) store.StoreChannel); ok {
+		r0 = rf(keyVal)
+	} else {
+		if ret.Get(0) != nil {
+			r0 = ret.Get(0).(store.StoreChannel)
+		}
+	}
+
+	return r0
+}