OpenAPI formatting linter (#3140)

## Description

Adds the `spectral` linter. `prettier` should be used as formatter.

The formatter is applied in
#3144.

~~`@redocly/openapi-cli` is chosen because it provides both a linter and
a built-in formatter while other linters suggest using `prettier`, which
provides less robust option compared to the `openapi-cli`.~~ Since the
tool is depricated, switched to `spectral` + `prettier`.

## Related Issues

Fixes #2971

.github/workflows/pull-request.yaml

@@ -176,10 +176,13 @@ jobs:
       - uses: actions/checkout@v4
         with:
           ref: ${{ github.event.pull_request.head.sha }}
-      - run: npm install @apidevtools/swagger-cli
+      - run: npm install @apidevtools/swagger-cli @stoplight/spectral-cli
       - run: node_modules/.bin/swagger-cli validate crates/orderbook/openapi.yml
       - run: node_modules/.bin/swagger-cli validate crates/driver/openapi.yml
       - run: node_modules/.bin/swagger-cli validate crates/solvers/openapi.yml
+      - run: node_modules/.bin/spectral lint crates/orderbook/openapi.yml
+      - run: node_modules/.bin/spectral lint crates/driver/openapi.yml
+      - run: node_modules/.bin/spectral lint crates/solvers/openapi.yml
 
   run-flaky-test:
     # to debug a flaky test set `if` to true and configure the flaky test in the `run` step

.spectral.yaml

@@ -0,0 +1 @@
+extends: "spectral:oas"