Please provide a way to refresh my ssh connection, or let me login/logout

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#### Description

I want to be able to edit the packer user's groups, then tell packer to refresh the ssh connection so that I don't have to do any hacky business to get my permissions -- I want to be able to tell packer to logout, and login.

#### Use Case(s)

I am building an EC2 image with a docker image on it. I have to run the docker commands as sudo.

#### Potential configuration

```
provisioner "shell" {
inline = [
"sudo usermod -a -G docker ec2-user"
]
}
# 2nd shell provisioner, that can be configured to refresh the connection
provisioner "shell" {
new_connection = true
inline = [
"docker run hello-world"
]
}

```

#### Potential References
This was brought up in an old thread of google groups.

https://groups.google.com/g/packer-tool/c/XPXwk7PgLcc

No source files or tests are named. Start at the shell provisioner and SSH connection lifecycle, then trace how a provisioner could request the refresh or logout/login behavior described by new_connection; done means a later Docker command uses the updated group permissions without a workaround.

Written by the indexing model from the issue text.