X-Correlator or x-correlator

[jlurien]

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"

[rartych]

Agree - to be considered in #188
We have also pending action : "X-Correlator header definition to be added to CAMARA_common.yaml" in minutes - we should define a common format in https://github.com/camaraproject/Commonalities/blob/main/artifacts/CAMARA_common.yaml

[PedroDiez]

Agree to align

[bigludo7]

Agree to align for me also.

[PedroDiez]

If no comments in different direction, a PR will be generated this week to align naming to "x-correlator" in design guidelines and also CloudEvent artifact