Add namespaces filtering to exclude `ProjectNamespaces` when fetching `Group`s

Before we can backfill a ProjectNamespace for each Project we need to ensure that current Namespace behaviours as Group or user namespace is kept, so we need to filter out ProjectNamespaces types from code where Group or user namespace is expected, related thread in a POC MR !70972 (diffs, comment 685493226)

• update APIs REST/GraphQL - acroitor - !71987 (merged)
• update group descendant/children queries - jprovaznik - !72119 (merged)
• update scopes in Namespace model - cablett
• routes autocomplete finder - jprovaznik - !72862 (merged)
• group transfer - !72863 (merged)
• CI minutes reset - !72980 (merged)