[RFE] Upgrade alert manager to 0.26.x

[MKlimuszka]

Components:

• [x] Bump the alertmanager image in the chart

  • Resolves CVEs
  • Allows users to consume the newer official configs like teams receivers into raw alertmanager configs stored in configmaps / secrets

• [ ] Bump the Alertmanager CRDs that contain the newer alertmanager config changes introduced in 0.26

  • Users can consume the the new configuration options via the CRDs

• [ ] Add UI for configuring the new options exposed in the alertmanager configs

  • Allows users to consume the new configuration options via the UI

• [ ] Documentation updates

• [ ] Deprecate the prom2teams alerting driver once the majority of the above items in this issue have been completed

• [ ] Remove the prom2teams alerting driver from the charts repo and from the alertmanager webhook UI

Backporting considerations

2.8.X