Restructure CLI code

[seriva]

• Restructure CLI code as last part of the repository overhaul started in 1.3.
• Refactor InitEngine class to be agnostic to changes in ApplyEngine and UpgradeEngine: Refactor InitEngine class to be agnostic to changes in ApplyEngine and UpgradeEngine #2944
• Removed epicli apply sleeps 10 seconds after creating inventory: [BUG] epicli apply sleeps 10 seconds after creating inventory #2945
• Rename __ping_retries to ping_retries for consistency.

@przemyslavic Attached are the original init outputs for every provider, full and non-full to compare against:

any-full.txt
any-minimal.txt
aws-full.txt
aws-minimal.txt
azure-full.txt
azure-minimal.txt

Note that the any-full.txt will be slightly different because its also merged now, rest should be all the same.

[przemyslavic]

Maybe this is a good opportunity to improve this timeout as well 😏
https://github.com/epiphany-platform/epiphany/blob/develop/cli/engine/providers/azure/APIProxy.py#L51

2:53:14 INFO cli.engine.providers.azure.APIProxy - Waiting 60 seconds...55
12:53:15 INFO cli.engine.providers.azure.APIProxy - Waiting 60 seconds...56
12:53:16 INFO cli.engine.providers.azure.APIProxy - Waiting 60 seconds...57
12:53:17 INFO cli.engine.providers.azure.APIProxy - Waiting 60 seconds...58
12:53:18 INFO cli.engine.providers.azure.APIProxy - Waiting 60 seconds...59
12:53:21 INFO cli.engine.providers.azure.APIProxy - Running: "az account set --subscription xxx"
12:53:21 INFO cli.engine.providers.azure.APIProxy - Done running "az account set --subscription xxx"

[seriva]

never

Maybe this is a good opportunity to improve this timeout as well 😏 https://github.com/epiphany-platform/epiphany/blob/develop/cli/engine/providers/azure/APIProxy.py#L51

2:53:14 INFO cli.engine.providers.azure.APIProxy - Waiting 60 seconds...55
12:53:15 INFO cli.engine.providers.azure.APIProxy - Waiting 60 seconds...56
12:53:16 INFO cli.engine.providers.azure.APIProxy - Waiting 60 seconds...57
12:53:17 INFO cli.engine.providers.azure.APIProxy - Waiting 60 seconds...58
12:53:18 INFO cli.engine.providers.azure.APIProxy - Waiting 60 seconds...59
12:53:21 INFO cli.engine.providers.azure.APIProxy - Running: "az account set --subscription xxx"
12:53:21 INFO cli.engine.providers.azure.APIProxy - Done running "az account set --subscription xxx"

This one I know for sure is actually needed, as Azure just doesn't propagate the SP in time before Terraform starts to run otherwise.

[przemyslavic]

But why 60 and not e.g. 20 🤔 I know it works fine with 60 for sure.
OK if it's more complex and there is no easy way to check SP availability, let's leave it as is.