feat(packer) create image galleries in the new subscription

[dduportal]

Ref. jenkins-infra/helpdesk#3818 (comment)

This PR creates the shared gallery in the new subscription:

• 3 resource groups (dev, staging and prod) with one gallery each
• 4 images on each gallery

IMPORTANT: this PR sets the ground to move everything to US East 2 (faster packer builds and we don't use East US since 1.5 years for agents). It cannot do all "eastus" -> "eastus2" changes yet though as changing location marks a resource group/gallery to be deleted, while we only want to create new resources (terraform forgets the old resource when only changing provider).

IMPORTANT (2): I've removed the 4 role assignments which are required for the 4 controllers (ci, trusted, cert and infra) to read the shared gallery to spin up agent. The build >= 3 for this PR should only mark 3 resources to delete (the role assignment of the packer_sp itself):

terraform state rm 'module.cert_ci_jenkins_io.azurerm_role_assignment.controller_read_packer_prod_images[0]'
terraform state rm 'module.trusted_ci_jenkins_io.azurerm_role_assignment.controller_read_packer_prod_images[0]'
terraform state rm 'module.ci_jenkins_io.azurerm_role_assignment.controller_read_packer_prod_images[0]'
terraform state rm 'azurerm_role_assignment.infra_ci_jenkins_io_allow_packer'

[dduportal]

Plan: 22 to add, 0 to change, 3 to destroy. as expected: self-merging (code was written and "terraform planned" in pair with @smerle33 )

[dduportal]

Errors while executing, like the following

│ Error: creating/updating Shared Image: (Image Name "jenkins-agent-ubuntu-22.04-arm64" / Gallery Name "dev_packer_images" / Resource Group "dev-packer-images"): compute.GalleryImagesClient#CreateOrUpdate: Failure sending request: StatusCode=404 -- Original Error: Code="ParentResourceNotFound" Message="Failed to perform 'write' on resource(s) of type 'galleries/images', because the parent resource '/subscriptions/<redacted>/resourceGroups/dev-packer-images/providers/Microsoft.Compute/galleries/dev_packer_images' could not be found."

Removed the galleries from state with:

for g in $(terraform state list | grep 'azurerm_shared_image');do terraform state rm "$g";done

New plan states: Plan: 15 to add, 0 to change, 0 to destroy., triggered a new build as it looks good

[dduportal]

New galleries created \o/