Release 1.9.1

[mickmister]

• https://github.com/mattermost/mattermost-plugin-gitlab/pull/491
• https://github.com/mattermost/mattermost-plugin-gitlab/pull/494
• https://github.com/mattermost/mattermost-plugin-gitlab/pull/495

[raghavaggarwal2308]

Closing as release is created https://github.com/mattermost/mattermost-plugin-gitlab/releases/tag/v1.9.1