Refactor routes init and add tests

[Tristan-WorkGH]

Some refactors:

• in GatewayConfig for bean myRoutes, no need to get manually each EndPointServer in Spring context, Spring can do it for us
  • add a test to check all EndPointServer are detected and set
• add test to check that filters are initialized and in correct order
• AbstractGlobalPreFilter don't need to be public, pass to package-only visibility
• remove redudant ExploreServer.hasElementsAccessControl having same body than parent EndPointElementServer
• fix some typos

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud