Merge branch '10-renovate-mattermost' into 'main'

SKIP UPDATE CHECK "Add renovate support for Mattermost Iron Bank images"

Closes #10

See merge request platform-one/big-bang/apps/collaboration-tools/mattermost!76

renovate.json

+{
+  "baseBranches": ["main"],
+  "configWarningReuseIssue": false,
+  "dependencyDashboard": "true",
+  "dependencyDashboardHeader": "- [ ] Follow steps in [package update docs](./docs/PACKAGE_UPDATES.md) to upgrade the package.",
+  "dependencyDashboardTitle": "Renovate: Upgrade Mattermost Package Dependencies",
+  "draftPR": true,
+  "enabledManagers": ["regex"],
+  "ignorePaths": ["chart/charts/**"],
+  "labels": ["mattermost","Package Sustainment","kind::chore"],
+  "packageRules": [
+    {
+      "matchDatasources": ["docker"],
+      "groupName": "Ironbank",
+      "registryUrls": ["https://registry1.dso.mil"]
+    }
+  ],
+  "separateMajorMinor": false,
+  "regexManagers": [
+    {
+      "fileMatch": ["^chart/values\\.yaml$"],
+      "matchStrings": [
+         "image:\\s+name:\\s+[^/]+/(?<depName>.+)\\s+tag:\\s+(?<currentValue>.+)"
+      ],
+      "depNameTemplate": "registry1.dso.mil/ironbank/opensource/mattermost/mattermost",
+      "datasourceTemplate": "docker"
+    }
+  ]
+}
+