Add support for completions in fish and powershell

[marckhouzam]

What this PR does / why we need it

This PR allows tanzu users to use shell completion for fish or powershell.
This is directly supported by Cobra and all this PR does is give access to the scripts.

Which issue(s) this PR fixes

Fixes #3158

Describe testing done for PR

Powershell:

$ pwsh
PS /Users/kmarc/git/tanzu-framework> ./tanzu <TAB>
# File completion is triggered.  This is not correct.

# Source the new completion script for powershell
PS /Users/kmarc/git/tanzu-framework> ./tanzu completion powershell | Out-String | Invoke-Expression
PS /Users/kmarc/git/tanzu-framework> ./tanzu <TAB>
completion  (Output shell completion code)                     init        (Initialize the CLI)
config      (Configuration for the CLI)                        plugin      (Manage CLI plugins)
context     (Configure and manage contexts for the Tanzu CLI)  update      (Update the CLI)
help        (Help about any command)                           version     (Version information)

Fish

$ fish
Welcome to fish, the friendly interactive shell
Type help for instructions on how to use fish
kmarc@kmarc-a01 ~/g/tanzu-framework (feat/compFish)> ./tanzu <TAB>
# File completion is triggered.  This is not correct.

# Source the new completion script for fish
kmarc@kmarc-a01 ~/g/tanzu-framework (feat/compFish)> ./tanzu completion fish | source
kmarc@kmarc-a01 ~/g/tanzu-framework (feat/compFish)> ./tanzu <TAB>
completion                  (Output shell completion code)  help  (Help about any command)  update        (Update the CLI)
config                         (Configuration for the CLI)  init      (Initialize the CLI)  version  (Version information)
context  (Configure and manage contexts for the Tanzu CLI)  plugin    (Manage CLI plugins)

Release note

The Tanzu CLI now supports shell completion for the fish shell and powershell.

Additional information

You can install powershell on Mac.

Special notes for your reviewer

Note also that with Cobra 1.5, it is no longer necessary to have zsh >= 5.2 (see spf13/cobra#1665).
So I have update the help text.

[codecov]

Codecov Report

Merging #3550 (53e538a) into main (a6760d3) will decrease coverage by 0.90%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #3550      +/-   ##
==========================================
- Coverage   46.55%   45.65%   -0.91%     
==========================================
  Files         400      425      +25     
  Lines       39706    41266    +1560     
==========================================
+ Hits        18486    18839     +353     
- Misses      19528    20716    +1188     
- Partials     1692     1711      +19     

Impacted Files	Coverage Δ
cli/core/pkg/command/completion.go	85.00% <100.00%> (+3.75%)	⬆️
packageclients/pkg/packageclient/package_update.go	83.57% <0.00%> (-1.43%)	⬇️
...ons/controllers/packageinstallstatus_controller.go	79.15% <0.00%> (-1.16%)	⬇️
addons/controllers/clusterbootstrap_controller.go	63.04% <0.00%> (-0.59%)	⬇️
cmd/cli/plugin/cluster/create.go	42.22% <0.00%> (ø)
cmd/cli/plugin/cluster/osimage.go	100.00% <0.00%> (ø)
cmd/cli/plugin/cluster/get_machinehealthcheck.go	11.42% <0.00%> (ø)
cmd/cli/plugin/cluster/get_node_pools.go	10.52% <0.00%> (ø)
cmd/cli/plugin/cluster/set_node_pool.go	14.63% <0.00%> (ø)
...md/cli/plugin/cluster/delete_machinehealthcheck.go	19.23% <0.00%> (ø)
... and 21 more

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[marckhouzam]

I will try to add tests to increase the code coverage

[chandrareddyp]

LGTM

[vuil]

Nice! Just a couple of nits on the comments in test.