pip state doesn't support salt global proxy

[Oloremo]

Description of Issue

There is an ability in Salt to sent minion wide http proxy:
#29322
#43764

https://docs.saltstack.com/en/latest/ref/configuration/minion.html#proxy-host

Setting this args will affect every module and state which is using a utils.http since it uses tornado by default and tornado is aware of those proxy options. pip module supports the separate proxy argument and I think kinda should support the system http_proxy variable but people report it's broken: #52186

I think the idea of global proxy is great I'd like other states to support it. So my proposal is to add a global proxy awareness for pip state.

Right now:

1. If proxy arg passed - add the proxy to the pip command

Will be:

1. If proxy arg passed and it's 'truthy" - add the proxy to the pip command
2. If proxy arg passed and it's False - disable proxy all together
3. If proxy not passed BUT global proxy set - use it to set up pip proxy

So the proxy arg still will be top priority and global proxy as a fallback plus the option to disable the proxy in a strange case when you have global proxy set but you dont want it to be applied to this particular state.

I already have a working patch and willing to implement it.

[Oloremo]

Feature merged!