Don't disable flag parsing on the root command

[marckhouzam]

The first commit of this PR is #594 for cobra 1.8.0

What this PR does / why we need it

This PR stops disabling flag parsing on the root CLI command to fix a small bug when updating to cobra 1.8.0.

I purposely kept this PR separate from #594 because even if we don't move to cobra 1.8.0, there is no reason for the CLI to disable flag parsing on its root command, as is explained below.

By disabling flag parsing on the root command, we tell Cobra not to parse flags when running the root command. Since there are are currently no flags on the root command this is not a problem. Furthermore, even with say, a global flag on the root command, this situation would still not be a problem because the root command is not actually runnable itself (no Run function), so flags would not be executed on the root command itself, but instead the DisableFlagParsing field would be read from the executable sub-command used.

However, there is an issue with not parsing flags on the root which is that it prevents Cobra's shell completion logic to complete the --help/-h flags on the root command. This is because all flag name completion becomes the responsibility of the program itself, and the program did not itself define --help/-h. This happens starting with Cobra v1.8.0.

We can see this by running tanzu __complete - and noticing the --help/-h flags are not suggested when using cobra 1.8.0.

The reason flag parsing was disabled on the root seems to be to allow plugins to handle their own flags. However, this is already done by each individual plugin sub-command created by GetCmdForPlugin() which does disable flag parsing already. There is therefore no reason to disable flag parsing on the root command.

Which issue(s) this PR fixes

Fixes # N/A

Describe testing done for PR

# Current behaviour of shell completion for the help flag on the root command
# This is correct, since the --help/-h flag is valid on the root command
$ git checkout main
$ make build
build darwin-arm64 CLI with version: v1.2.0-dev
mkdir -p bin
cp /Users/kmarc/git/tanzu-cli/artifacts/darwin/arm64/cli/core/v1.2.0-dev/tanzu-cli-darwin_arm64 ./bin/tanzu
$ tz __complete -
--help	help for tanzu
-h	help for tanzu
:4
Completion ended with directive: ShellCompDirectiveNoFileComp

# New behaviour of shell completion once we move to cobra 1.8.0
# This is now wrong as the --help/-h are not longer completed
$ git checkout feat/cobra1.8.0
Switched to branch 'feat/cobra1.8.0'
$ make build
build darwin-arm64 CLI with version: v1.2.0-dev
mkdir -p bin
cp /Users/kmarc/git/tanzu-cli/artifacts/darwin/arm64/cli/core/v1.2.0-dev/tanzu-cli-darwin_arm64 ./bin/tanzu
$ tz __complete -
:4
Completion ended with directive: ShellCompDirectiveNoFileComp

# Fix for this issue
$ git checkout fix/compDoubleHelpFlagForPlugins
Switched to branch 'fix/compDoubleHelpFlagForPlugins'
$ make build
build darwin-arm64 CLI with version: v1.2.0-dev
mkdir -p bin
cp /Users/kmarc/git/tanzu-cli/artifacts/darwin/arm64/cli/core/v1.2.0-dev/tanzu-cli-darwin_arm64 ./bin/tanzu
$ tz __complete -
--help	help for tanzu
-h	help for tanzu
:4
Completion ended with directive: ShellCompDirectiveNoFileComp

Release note

Don't disable flag parsing on the root command.

Additional information

Special notes for your reviewer

[anujc25]

LGTM. Thanks for explaining all the details as part of the description along with testing information.