Add IANA and RFC References to status Codes

[BirgitBoss]

What?

We may add the following references for status codes:

https://www.iana.org/assignments/http-status-codes/http-status-codes.xhtml
https://www.rfc-editor.org/rfc/rfc9110.html

They are mentioned in the changelog, e.g. https://industrialdigitaltwin.io/aas-specifications/IDTA-01002/v3.1/changelog.html#_changes_w_r_t_v3_0_to_v3_0_1 but not in the documentation itself

[sebbader-sap]

I can't find any explicit reference to the IANA resource. And as also the RFC9110 appearance in the ChangeLog is not adding additional value but only containing the consensus and best practices which are the foundations of the AAS API, I'll close this issue.
Feel free to open it again, but my current feeling is that adding both references in the current state of the specification would require additional explanation to prevent a confusion of the reader.