Breaking change: Use consistent ID naming

[koplas]

Currently, there are some linter warnings about the naming of struct fields:

csaf/advisory.go:449:2: struct field ProductIds should be ProductIDs
csaf/advisory.go:612:2: struct field GroupIds should be GroupIDs
csaf/advisory.go:613:2: struct field ProductIds should be ProductIDs
csaf/advisory.go:744:2: struct field GroupIds should be GroupIDs
csaf/advisory.go:745:2: struct field ProductIds should be ProductIDs

Changing the names will result in a breaking change.

[bernhardreiter]

Changing the name to break the API does not seem worth a new major, so what about silencing the warnings until we do a major version?