[FEAT]: Tab completion

[hansfn]

Describe the need

Tab completion is missing for "gh copilot". Compare gh copilot with gh workflow. (Showing the output of the __complete command.)

$ gh __complete copilot  ''
:0
Completion ended with directive: ShellCompDirectiveDefault

$ gh __complete workflow  ''
disable Disable a workflow
enable  Enable a workflow
list    List workflows
run     Run a workflow by creating a workflow_dispatch event
view    View the summary of a workflow
:4
Completion ended with directive: ShellCompDirectiveNoFileComp

Version

Tested with v1.0.5