ERP5Site_checkOAuth2ResourceServerPostUpgradeConsistency: Do not lock ERP5 users out

When there is no enabled extractor plugin, PAS internally uses the DumbHTTPExtractor
class. When installing the OAuth2 resource server plugin, it activates itself as an extractor,
disabling this default mechanism. This is most likely unexpected to the admin, so in such
situation create & enable the ERP5 plugin which inherits from DumbHTTPExtractor, to
preserve basic authentiation.
If such plugin exists but is disabled, assume the admin forgot to enable it, and do it for them.
If any extraction plugin is already enabled, do nothing new.