Align API spec format with the latest Commonalities agreements

[jpengar]

Address issue #33

Align API spec format with the latest Commonalities agreements:

• Commonalities - adjust the error status field, which will eventually be an integer (not a patterned string): PR #145.
• Commonalities - adjust the schema references in the errors responses and apply the agreed solution: Issue #151 & PR #162.
• Commonalities - change the format of the API fields to lowerCamelCase: Issue #157, Discussion #169 & PR #171.

In addition, this PR includes:

• Some minor tweaks to non-functional definitions in the API spec (e.g. reusing the x-correlator definition).
• Removal of max_allowed missed as part of RFC4594 related changes made as a result of issue #23.

[bigludo7]

Look good for me. Thanks

[rartych]

I have doubts about adding the definition of X-Correlator header. See https://github.com/camaraproject/WorkingGroups/blob/main/Commonalities/documentation/API-design-guidelines.md#9-architecture-headers and the Eric's comment in
camaraproject/WorkingGroups#124
The reason I originally raised this issue was to get an agreement on which headers should explicitly be included in OAS API definition files. And the answer is "None of the headers listed in the API Design Guidelines".

[monamok]

I have doubts about adding the definition of X-Correlator header.

Hello @rartych, the headers that should not be included in the defenitions are standard headers specified in section 3.5 where it says: "To avoid cluttering the CAMARA OAS (Swagger) definition files, the above headers must not be included explicitly in the API definition files even when supported, as it can be assumed that developers will already be familiar with their use."
x-correlator comes in section 9 and can be included.

[monamok]

@bigludo7 could you please review the changes and share your feedback? Thank you.

[rartych]

LGTM.