added sys.shell changes to allow token usage in its user context if a…

[KS-7250]

What type of PR is this?

/kind feature

What this PR does / why we need it:

Realm now has a global token store, but no way to use it. This PR allows the sys.shell() function to take permissions from the active token and apply it to the context of the command run.

In this example, let's say pid 700 is a SYSTEM process, and we impersonated it from Administrator:

$> sys.tokens()

| active | id | source              |
| ------ | -- | ------------------- |
| True   | 1  | impersonate:pid:700 |

$> sys.shell('whoami')['stdout']

nt authority\system

Which issue(s) this PR fixes:

N/A