Consider providing cloud images

**Is your feature request related to a problem? Please describe.**
Currently we recommend using [Bitnami](https://bitnami.com/stack/weblate) for cloud deployments. It has however some problems:

* Their images are outdated (eg. [Azure Marketplace](https://azuremarketplace.microsoft.com/en-us/marketplace/apps/bitnami.weblate) lists 3.6)
* ~~They are still on Python 2.7 (at least it looks so from the docs)~~ (it's only outdated docs, even the Azure 3.6 image runs on Python 3.7)
* They suggest to [modify Django defaults to change configuration](https://docs.bitnami.com/general/apps/weblate/configuration/configure-smtp/) - *the settings are gone after Django upgrade*
* [Obsolete upgrading instructions](https://docs.bitnami.com/general/apps/weblate/administration/upgrade/) which probably made sense when switching from South to Django years ago, but today are just confusing
* Several warnings right on installation:
* Celery is configured in the eager mode - *serious performance issues*
* The cookie secret key has default value - *can have security implications, fortunately it's not used in default setup*
* Path /opt/bitnami/apps/weblate/weblate/data/vcs is not writable, check your DATA_DIR settings. (tons of these) - *can lead to some breakages during runtime, though it seems to be just wrong owner in this case as writing to it doesn't fail*

**Describe the solution you'd like**
Investigate options how to provision official images for some widely used platforms (the actual list is to be investigated, but what comes to my mind is: AWS, Azure, Digital Ocean, GCP)

**Describe alternatives you've considered**
We might also cooperate with Bitnami to bring their image to better shape.