As a Security Server user I want that X-Road metaservice codes are reserved so that the user can't overload them

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X-Road metaservices use predefined service codes (listClients, listCentralServices, listMethods, allowedMethods, getWsdl and getOpenAPI) as described in service metadata protocol documents for SOAP and REST. However, currently it is possible for the user to add their own service with same service code as the metaservices. In this task, the metaservice service codes should be reserved so that the user can't add such SOAP or REST services that use reserved service codes.

The JIRA ticket this issue was created from can be found here: https://nordic-institute.atlassian.net/browse/XRDDEV-599

Acceptance criteria:

• [ ] SOAP metadata service codes are reserved so that users can't add their own services with the same codes
  • listClients, listCentralServices, listMethods, allowedMethods and getWsdl
• [ ] REST metadata service codes are reserved so that users can't add their own services with the same codes
  • listClients, listCentralServices, listMethods, allowedMethods and getOpenAPI
• [ ] The Security Server user manual and metadata protocol documents are updated with the relevant information:
  • [ ] https://github.com/nordic-institute/X-Road/blob/develop/doc/Manuals/ug-ss_x-road_6_security_server_user_guide.md#6-x-road-services
  • [ ] https://github.com/nordic-institute/X-Road/blob/develop/doc/Protocols/pr-meta_x-road_service_metadata_protocol.md
  • [ ] https://github.com/nordic-institute/X-Road/blob/develop/doc/Protocols/pr-mrest_x-road_service_metadata_protocol_for_rest.md