Clarify behaviour of cmdlet `Update-SessionEnvironment`

### Checklist

- [x] I have verified this is the correct repository for opening this issue.
- [x] I have verified no other issues exist related to my request.

### Is Your Feature Request Related To A Problem? Please describe.

When a maintainer or user makes use of the `Update-SessionEnvironment` variable, they may think that it will affect the running session of the users PowerShell session, instead of just the session that the package is running in.

### Describe The Solution. Why is it needed?

We need to clarify what we are talking about when mentioning the current session when the `Update-SessionEnvironment` cmdlet is being used, and who or what will see the changes that gets updated/refreshed.

For example, if the `Update-SessionEnvironment` is being called inside of a package, only the package that calls it will have any updated or refreshed environment variables, other remaining packages that gets installed will be unaffected, as well as the user session that called `choco` will also be unaffected and need to call the same cmdlet themself.

### User Story

I as a maintainer of Chocolatey packages
want to know what gets affected
so I can take appropriate measures during decisions in the package, or recommendations to the user.

### Additional Context

The page that needs to be updated is: https://docs.chocolatey.org/en-us/create/cmdlets/update-sessionenvironment/

After that is updated, the next version of Chocolatey CLI needs to have the help documentation re-generated.

This issue was created as part of a comment made by a user recommending clarifications: https://github.com/chocolatey/choco/issues/3865#issuecomment-4197549374

### Acceptance Criteria

- [ ] Documentation has been updated with a clarification

### Related Issues

https://github.com/chocolatey/choco/issues/3865

Start with the documented page at docs.chocolatey.org/en-us/create/cmdlets/update-sessionenvironment/ and review how it currently describes the current session and affected environment variables. Update the page to clarify the package, other packages, and calling user session, then account for the requested regeneration of Chocolatey CLI help documentation.

Written by the indexing model from the issue text.