Problem description
Guidelines in Commonalities specifies "X-Correlator" but almost all API specs define already "x-correlator"

Expected behavior
Even if header name is case insensitive and both options are interoperable, we should define a common behaviour for coherence, aligned with Guidelines.

As de facto API specs are using "x-correlator", it would be less effort to reflect this in the Guidelines.

It would be convenient to set a new linting rule to check that the header is included in the requests and responses, following the agreed format.

Alternative solution
Adjust all APIs using "x-correlator"