Allow `+` for deep customizations on `core:install`

[totten]

Background: In several commands (api3, api4, setting:set), there are two kinds of options:

• Control options: Arguments like --level, --out, -T, --user, --cwd, --hostname influence the way that cv works. The naming / formatting / behavior of the options are primarily driven by cv.
• Data model options: Arguments like +s field_1,field2 influence the data that cv passes through to civicrm.The naming / formatting / behavior are primarily driven by CiviCRM's model. The convention here is tuned for "adding data to a request-document". If you need to get really detailed, it allows JSON.

Problem: The core:install command has a mix of control options and data model options. But the data-model options don't follow the + convention; they miss a bunch of edge-cases; and they don't allow JSON. The same is true of core:check-req and core:uninstall.

Example: Currently, you can use cv path -m X=Y, but there's no way to set a value for $setup->model['paths']['civicrm.files'].

Idea: In the same vein as SettingArgParser or Api4ArgParser, add a SetupModelParser to allow more inputs. Follow the same + conventions as the other commands.

[demeritcowboy]

Related, or actually probably the same thing: https://github.com/civicrm/cv/issues/72

[totten]

Right as usual @demeritcowboy. The first issue says, "I'm hungry"; and the second issue says, "Get a slice of pizza".

[demeritcowboy]

🇭🇺 🍕