Is your feature request related to a problem? Please describe.
Today Harbor requires Docker and docker-compose for installations and upgrades.

https://github.com/goharbor/harbor/blob/master/make/common.sh#L78-L130
https://github.com/goharbor/harbor/blob/master/README.md#install--run

Red Hat has deprecated and removed Docker since RHEL8 :-(
https://access.redhat.com/solutions/3696691

While Docker (the company) is still shipping CE and EE binaries for RHEL, the lack of official support from Red Hat may be a source of conflict.

This proposal is to support also Podman as a container Engine. This is not only in favor of Red Hat but more generally of the added security features of Podman.
http://people.redhat.com/abach/OSAW/FILES/DAY1/5%20Moving%20on%20from%20Docker.pdf

Describe the solution you'd like
Since Podman 3.0, docker-compose is fully supported
https://www.redhat.com/sysadmin/podman-docker-compose

Perhaps the logic at check_docker in common.sh could be reworked to also support Podman

Describe the main design/architecture of your solution
Podman supports docker alias but using Podman CLI would be best.
The idea would be to first rework the logic in check_docker verifying whether Docker is present and meet the minimum version and same story to Podman.

Describe the development plan you've considered
Assuming the proposal is acceptable, I can work on a prototype solution and have something available in a few weeks (the logic isn't that hard but perhaps there are all sort of documentation references to update)