Check for icon links on registry build to avoid missing icon links

[elsony]

Which area/kind this issue is related to?

/area registry

Issue Description

The existing registry build does not check if the icons for a stack/sample are valid and exist or not. This leads to some potential problems that the icon in the registry of a given may be missing, e.g. #1023.

To prevent this to happen in the future, we should

1. check to make sure the icons are valid during the registry build and fail the registry build if the icons are missing.
2. see if we can package the icons inside the registry build

Edit by thepetk
Target date: 16/3/2023

[thepetk]

Closed after the merge of devfile/registry-support#167