Add support for project traces via GraphQL

What does this MR do and why?

• Adds a new observabilityTracesLinks GraphQL edge to ProjectType.
• Adds required types and resolver to implement it.
• Adds specs, including changes to other files as well as request specs for the new GraphQL interface.

Database queries

All records for a project

(These are from locally generated data since the table is brand new)

This query reads from an index condition as expected.

SELECT "observability_traces_issues_connections".* FROM "observability_traces_issues_connections" WHERE "observability_traces_issues_connections"."project_id" = 15;

                                                                       QUERY PLAN
                                         QUERY PLAN
---------------------------------------------------------------------------------------------
 Seq Scan on observability_traces_issues_connections  (cost=0.00..129.50 rows=5000 width=77)
   Filter: (project_id = 15)
(2 rows)

### Selecting an individual record for a project

Query uses same index condition as above, and then filters on specific criteria. This will likely never return more than 1 or 2 records.

```sql
SELECT "observability_traces_issues_connections".* FROM "observability_traces_issues_connections" WHERE "observability_traces_issues_connections"."project_id" = 15 AND "observability_traces_issues_connections"."trace_identifier" = '46c0d0dc-b3af-4a3b-be80-b15ae022bfcc' LIMIT 1

                                                                          QUERY PLAN
--------------------------------------------------------------------------------------------------------------------------------------------------------------
 Limit  (cost=0.28..93.80 rows=1 width=77)
   ->  Index Scan using idx_o11y_trace_issue_conn_on_issue_id_trace_identifier on observability_traces_issues_connections  (cost=0.28..93.80 rows=1 width=77)
         Index Cond: (trace_identifier = '46c0d0dc-b3af-4a3b-be80-b15ae022bfcc'::text)
         Filter: (project_id = 15)

MR acceptance checklist

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Screenshots or screen recordings

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Before	After

How to set up and validate locally

1. Ensure you're using an Ultimate namespace.

2. Enable the :observability_features feature flag.

3. Create a new project, within an Ultimate group.

4. Create a new issue, and note its ID.

5. On a rails console, create a linked log for that project.

   issue_id = {{ID}}
   a = a = Observability::TracesIssuesConnection.create(issue: Project.find(issue_id).issues.last, trace_identifier: 'xxxxxx')
   a.save! # Raise an exception if something went wrong.

6. For the created log, we can query a list of links - note the format of the timestamp should be iso8601.

   query {
     project(fullPath: "Flightjs/Flight") {
       id
       observabilityTracesLinks {
         nodes {
           traceIdentifier
           issue {
             title
             webUrl
           }
         }
       }
     }
   }

7. If successful, it should return a list of observabiltyLogsLinks, each representing the link between an observabililtyLog and its issue (if queried, as above)

   {
     "data": {
       "project": {
         "id": "gid://gitlab/Project/7",
         "observabilityTracesLinks": {
           "nodes": [
             {
               "traceIdentifier": "23489affd",
               "issue": {
                 "title": "fdfsdfsdfsdfsdfs",
                 "webUrl": "http://127.0.0.1:3000/flightjs/Flight/-/issues/40"
               }
             }
           ]
         } 
       }
     }
   }

Related to gitlab-org/opstrace/opstrace#2904 (closed)