Support image lookup by tags

[pborn-ionos]

Reference: https://github.com/ionos-cloud/cluster-api-provider-ionoscloud/blob/main/docs/custom-image.md#enabling-image-lookup

CAPIC already supports referencing templates by label, instead of requiring the user to supply the UUID of the image. Since Proxmox also supports tags on VMs, we should also support referencing the template by tags, rather than requiring supplying the VMID of the template VM.