cli: fix cli completion setup for zsh

[dvdksn]

Autocomplete was not set up correctly when tilde was used in FPATH.

Changed the .zshrc config to use $HOME instead (and quoting the heredoc delimiter to escape env vars)

• Closes Tilde used in zsh completion leads to misconfiguration #21060

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[thaJeztah]

Wondering if we can use the instruction from the completions command itself;

docker completion zsh --help

Usage:  docker completion zsh

Generate the autocompletion script for the zsh shell.

If shell completion is not already enabled in your environment you will need
to enable it.  You can execute the following once:

	echo "autoload -U compinit; compinit" >> ~/.zshrc

To load completions in your current shell session:

	source <(docker completion zsh)

To load completions for every new session, execute once:

#### Linux:

	docker completion zsh > "${fpath[1]}/_docker"

#### macOS:

	docker completion zsh > $(brew --prefix)/share/zsh/site-functions/_docker

You will need to start a new shell for this setup to take effect.

[dvdksn]

docker completion zsh > "${fpath[1]}/_docker"

I don't particularly love this. Maybe because I am not a zsh user, but I think the version in these docs are clearer.

[sarahsanders-docker]

LGTM