CLOUDP-288860: Update IPA exception format

[lovisaberggren]

Proposed changes

Updated the spec with a change to the exception format, now the exceptions are formatted as follows:

"x-xgen-IPA-exception": {
  "xgen-IPA-104-resource-has-GET": "Legacy API, not used by infrastructure-as-code tooling",
  "xgen-IPA-105-resource-has-LIST": "Legacy API, not used by infrastructure-as-code tooling"
},

Previously:

"x-xgen-IPA-exception": {
  "xgen-IPA-104-resource-has-GET": {
    "reason": "Legacy API, not used by infrastructure-as-code tooling"
  },
  "xgen-IPA-105-resource-has-LIST": {
    "reason": "Legacy API, not used by infrastructure-as-code tooling"
  }
},

• Updated the exception format validation to validate the new format
• Updated exceptions in tests

Jira ticket: CLOUDP-288860

[wtrocki]

Super nice change! Thank you