Fix missing completion for 'SpaceSupporter'

[marckhouzam]

Description of the Change

Missing space-role "SpaceSupporter" in the completion choices.
This was forgotten in #2176

Why Is This PR Valuable?

Helps the users that use shell completion for the set-space-role and unset-space-role.

Applicable Issues

List any applicable GitHub Issues here

How Urgent Is The Change?

Not urgent

Manual testing

$ cat ~/cf.zsh
# zsh completion for Cloud Foundry CLI

_cf-cli() {
    # All arguments except the first one
    args=("${COMP_WORDS[@]:1:$COMP_CWORD}")
    # Only split on newlines
    local IFS=$'\n'
    # Call completion (note that the first element of COMP_WORDS is
    # the executable itself)
    COMPREPLY=($(GO_FLAGS_COMPLETION=1 ${COMP_WORDS[0]} "${args[@]}"))
    return 0
}
autoload -U +X bashcompinit && bashcompinit
complete -F _cf-cli cf

$ source ~/cf.zsh

$ out/cf set-space-role [email protected] cli-org SP1 Space<TAB>
SpaceAuditor    SpaceDeveloper  SpaceManager    SpaceSupporter

[gururajsh]

LGTM