fix: Fix handling unavailable services

[pj892031]

Description

The new Gateway contains a couple of bugs about unavailable services. The response of Gateway is incorrect:

• when no ZAAS is onboarded and the request treatment requires any it returns 503, but if the ZAAS is onboarded and down, the authentication treatment is omitted
  • now response code 503 is always (if there is no onboarded ZAAS or all are down)
• if the first ZAAS is down, the rest are not called and GW returns 500
  • the fix skip the invalid call and try the next one
• if a service instance is down the load balancer does not try the next instance
  • the impact is limited because of repeating (see 5 attempts)
  • the fix skip unavailable service and try the next one
• error handling of ServiceNotAccessibleException is incorrect
  • it generates a mix of 500 and 503 responses because of missing argument URL
  • fix to show the correct message
• the response from ZAAS other than 401 and 200 is incorrectly processed in case of the latest instance to try a call
  • it could lead to propagating wrong credentials (ie. Basic null:null for passticket)

Linked to #3871 (a follow up of #3871)

Type of change

Please delete options that are not relevant.

• fix: Bug fix (non-breaking change which fixes an issue)
• feat: New feature (non-breaking change which adds functionality)
• docs: Change in a documentation
• refactor: Refactor the code
• chore: Chore, repository cleanup, updates the dependencies.
• BREAKING CHANGE or !: Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the style guidelines of this project
• PR title conforms to commit message guideline ## Commit Message Structure Guideline
• I have commented my code, particularly in hard-to-understand areas. In JS I did provide JSDoc
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• The java tests in the area I was working on leverage @nested annotations
• Any dependent changes have been merged and published in downstream modules

For more details about how should the code look like read the Contributing guideline

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
93.8% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud