feat: instance requests implementation for resource API (#9830)

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# Which Problems Are Solved

These changes introduce resource-based API endpoints for managing
instances and custom domains.

There are 4 types of changes:

- Endpoint implementation: consisting of the protobuf interface and the
implementation of the endpoint. E.g:
606439a172
- (Integration) Tests: testing the implemented endpoint. E.g:
cdfe1f0372
- Fixes: Bugs found during development that are being fixed. E.g:
acbbeedd32
- Miscellaneous: code needed to put everything together or that doesn't
fit any of the above categories. E.g:
529df92abc or
6802cb5468

# How the Problems Are Solved

_Ticked checkboxes indicate that the functionality is complete_

- [x] Instance
  - [x] Create endpoint
  - [x] Create endpoint tests
  - [x] Update endpoint
  - [x] Update endpoint tests
  - [x] Get endpoint
  - [x] Get endpoint tests
  - [x] Delete endpoint
  - [x] Delete endpoint tests
- [x] Custom Domains
  - [x] Add custom domain
  - [x] Add custom domain tests
  - [x] Remove custom domain
  - [x] Remove custom domain tests
  - [x] List custom domains
  - [x] List custom domains tests
- [x] Trusted Domains
  - [x] Add trusted domain
  - [x] Add trusted domain tests
  - [x] Remove trusted domain
  - [x] Remove trusted domain tests
  - [x] List trusted domains
  - [x] List trusted domains tests

# Additional Changes

When looking for instances (through the `ListInstances` endpoint)
matching a given query, if you ask for the results to be order by a
specific column, the query will fail due to a syntax error. This is
fixed in acbbeedd32 . Further explanation
can be found in the commit message

# Additional Context

- Relates to #9452 
- CreateInstance has been excluded:
https://github.com/zitadel/zitadel/issues/9930
- Permission checks / instance retrieval (middleware) needs to be
changed to allow context based permission checks
(https://github.com/zitadel/zitadel/issues/9929), required for
ListInstances

---------

Co-authored-by: Livio Spring <livio.a@gmail.com>

docs/docusaurus.config.js

@@ -364,6 +364,14 @@ module.exports = {
               categoryLinkSource: "auto",
             },
           },
+          instance_v2: {
+            specPath: ".artifacts/openapi/zitadel/instance/v2beta/instance_service.swagger.json",
+            outputDir: "docs/apis/resources/instance_service_v2",
+            sidebarOptions: {
+              groupPathsBy: "tag",
+              categoryLinkSource: "auto",
+            },
+          },
         },
       },
     ],