Update Azure frontend cache invalidator to use the newest Azure SDK

[tm-kn]

• Make Azure front-end cache invalidator compatible with the newest version of SDK packages.
  • Removes CUSTOM_HEADERS setting as that is no longer supported.
• This will make it incompatible with the old Azure SDKs. Given we don't enforce versions this may be problematic. I can't see a benefit of maintaining the old version support given how recently this has been added to Wagtail.

PR that originally added the Azure backend: #6119.

Testing locally

You will need Azure CDN and Front Door services provisioned.

Install the SDK libraries.

azure-mgmt-cdn
azure-mgmt-frontdoor

Set up the backend in you settings.

WAGTAILFRONTENDCACHE = {
    'azure_cdn': {
        'BACKEND': 'wagtail.contrib.frontend_cache.backends.AzureCdnBackend',
        'RESOURCE_GROUP_NAME': '',
        'CDN_PROFILE_NAME': '',
        'CDN_ENDPOINT_NAME': '',
    },
    'azure_front_door': {
        'BACKEND': 'wagtail.contrib.frontend_cache.backends.AzureFrontDoorBackend',
        'RESOURCE_GROUP_NAME': '',
        'FRONT_DOOR_NAME': '',
    }
}

Test purging in your ./manage.py shell.

from  wagtail.contrib.frontend_cache.utils import get_backends

fd = get_backends()['azure_front_door']
fd.purge("/test/")

cdn = get_backends()['azure_cdn']
cdn.purge("/test/")

[squash-labs]

Manage this branch in Squash

Test this branch here: https://tm-knfeatureupdate-azure-cdn-725xm.squash.io

[lb-]

Call out for anyone familiar with Azure to review this PR - maybe @chosak @jacobtoppm or @FlipperPA