Support configuring multiple default trusted registry for plugin downloads during build-time

[anujc25]

What this PR does / why we need it

• When building the tanzu-cli, by default we used to select TKG_DEFAULT_IMAGE_REPOSITORY as a default registry that we should trust when downloading the plugins. Also during build time TKG_DEFAULT_IMAGE_REPOSITORY we can only take 1 repository.

• This change introduces more flexibility by introducing another TANZU_PLUGINS_ALLOWED_IMAGE_REPOSITORIES variable that can have multiple image repositories with comma separated strings.

Which issue(s) this PR fixes

Fixes #2978

Describe testing done for PR

• Build the tanzu-cli by configuring TANZU_PLUGINS_ALLOWED_IMAGE_REPOSITORIES=projects.registry.vmware.com/tkg,projects.registry.vmware.com/vsphere
• Verified that user is able to download plugins from both registries without configuring any additional environment variables

Release note

Support configuring multiple default trusted registry for plugin downloads during build-time using `TANZU_PLUGINS_ALLOWED_IMAGE_REPOSITORIES`

Additional information

Special notes for your reviewer

[codecov]

Codecov Report

Merging #2977 (79084cd) into main (6d6ca50) will increase coverage by 0.03%.
The diff coverage is 0.00%.

❗ Current head 79084cd differs from pull request most recent head 4dcb262. Consider uploading reports for the commit 4dcb262 to get more accurate results

@@            Coverage Diff             @@
##             main    #2977      +/-   ##
==========================================
+ Coverage   44.00%   44.04%   +0.03%     
==========================================
  Files         416      416              
  Lines       41852    41850       -2     
==========================================
+ Hits        18417    18432      +15     
+ Misses      21714    21702      -12     
+ Partials     1721     1716       -5     

Impacted Files	Coverage Δ
pkg/v1/config/defaults.go	42.30% <0.00%> (-0.83%)	⬇️
addons/controllers/addon_controller.go	63.30% <0.00%> (-0.31%)	⬇️
addons/controllers/clusterbootstrap_controller.go	64.96% <0.00%> (+1.05%)	⬆️
...ons/controllers/packageinstallstatus_controller.go	82.79% <0.00%> (+2.15%)	⬆️

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[vuil]

lgtm, thanks

[vijaykatam]

codecov check fail is due to codecov/codecov-action#788

[vuil]

@anujc25 good to mention TANZU_PLUGINS_ALLOWED_IMAGE_REPOSITORIES in the release notes section.
codecov error not related to the change. PR is good to merge.