show config now shows all config, filter-able, contains host tox python and package versions

[gaborbernat]

--showconfig overhaul:

• now fully generated via the config parser, so anyone can load it by using the built-in python config parser
• the tox section contains all configuration data from config
• the tox section contains a host_python key detailing the path of the host python
• the tox:version section contains the versions of all packages tox depends on with their version
• passing -l now allows only listing default target envs
• allows showing config for a given set of tox environments only via the -e cli flag or the TOXENV environment variable, in this case the tox and tox:version section is only shown if at least one verbosity flag is passed

[asottile]

neat, fixnship

[gaborbernat]

Argh Azure decided to go down again in West Europe 🤦‍♂ https://status.dev.azure.com/_event/120579265