Added Documentaion Comments for SSH Tunnel flags

Updated the `doc.go` file to adhere to
[Go Doc Comment](https://go.dev/doc/comment) syntax. This allows
the documentation to render correctly on `pkg.go.dev`.

I was reading the `multistep` package documentation when I noticed
this. Perhaps there are more packages that need updating but I didn't
enumerate them.

I am adding the changes to handle the ssh-agent forwarding in windows, before this changes the packer code would always go and check the SSH_AUTH_SOCK environment variable for socket file, which is the behavior in linux but in windows a named static files gets used for this purpose, so have added changes for the same.

This was reported by multiple users for reference i have added the github issue link above.

Tests:
Have added the Unit Test cases for the new changes.

* correcting path for user_data_file

* updating go mod

* updating path

* updating source ami for windows

* fixing package import

* adding skip_create_ami to avoid creating AMI in acceptance test.

Deprecating `Message` method in UI interface

Bump golang /x/net to 0.38

Pin actions to address security scanner

* chore: update pr template for PCI

* chore: update pr template for PCI

Added the SensitiveVarsConfigKey