Update pkispawn to support ACME

[edewata]

pkispawn has been modified to support installing ACME in a shared PKI server (e.g. with existing CA).

New pkispawn params have been added to specify the ACME database, issuer, and realm. A sample configuration has been provided in acme.cfg.

The pki_ds_setup, pki_security_domain_setup, and pki_registry_enable params in the default.cfg have been moved from [DEFAULT] into each subsystem's section so that ACME can skip DS setup, security domain setup, and registry setup by default.

The config templates for ACME database, issuer, and realm have been modified to no longer contain passwords. The passwords will need to be specified during installation.

Some code in acme.py has been moved into subsystem.py so that it can be reused.

The basic ACME test and the test with PostgreSQL have been modified to install ACME using pkispawn.

[fmarco76]

I am not familiar with ACME but the code looks good. I have a comment for the configuration properties but feel free to merge and discuss later further changes.

[fmarco76]

Why these parameters are not included with default empty value?

All parameters start with pki_ while these starts with acme_. Actually I think start the subsystem variable with <subsystem>_ and leave pki_ to the global section could be better but I like consistency more.

[sonarcloud]

Quality Gate passed

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[edewata]

@fmarco76 Thanks! I've fixed some pylint issues. I'll merge but feel free to continue the discussion.

There's no default params for database/issuer/realm since the _type param cannot be blank and other params are only required depending on which type is selected so it's probably better to just explain it in the doc and let the user specify the params they need. The doc will be updated separately later.

I was considering to use pki_ prefix too but it seems kind of long (e.g. pki_acme_database_type) and redundant, but I don't have a strong opinion on this. If you prefer to use the pki_ prefix just let me know, we can add it in a separate PR.