Use errors dictionaries for community program components

We need to follow the project style guidelines for error handling and use shared error dictionaries instead of local component-based constants to avoid duplicates. See example here.

This issue covers components under ~/javascripts/subscription/components/community_program/.

More information in the original thread here: https://gitlab.com/gitlab-com/marketing/developer-relations/strategy-programs/open-source-program/gitlab-for-open-source/-/issues/51#note_2473519230