mattermost update to 11.5.1-bb.2

Package Merge Request

Package Changes

https://repo1.dso.mil/big-bang/product/packages/mattermost/-/blob/11.5.1-bb.2/CHANGELOG.md

Package MR

big-bang/product/packages/mattermost!356 (merged)

For Issue

big-bang/product/packages/mattermost#233 (closed)

Upgrade Notices

Mattermost license secret can now be provided as an existing secret rather than provided via helm values. Remove license value and provide the mattermost package values with addons.mattermost.enterprise.existingSecret. Existing method of creating license secret via helm values will continue to work without interruption.

```

addons:
 mattermost:
 enterprise:
 enabled: true
 existingSecret: <insertExistingSecretName>

```