[deps]: Bump openApiVersion from 2.1.0 to 2.6.0

Bumps `openApiVersion` from 2.1.0 to 2.6.0.

Updates `org.springdoc:springdoc-openapi-starter-common` from 2.1.0 to 2.6.0
- [Release notes](https://github.com/springdoc/springdoc-openapi/releases)
- [Changelog](https://github.com/springdoc/springdoc-openapi/blob/main/CHANGELOG.md)
- [Commits](springdoc/springdoc-openapi@v2.1.0...v2.6.0)

Updates `org.springdoc:springdoc-openapi-starter-webmvc-ui` from 2.1.0 to 2.6.0
- [Release notes](https://github.com/springdoc/springdoc-openapi/releases)
- [Changelog](https://github.com/springdoc/springdoc-openapi/blob/main/CHANGELOG.md)
- [Commits](springdoc/springdoc-openapi@v2.1.0...v2.6.0)

---
updated-dependencies:
- dependency-name: org.springdoc:springdoc-openapi-starter-common
  dependency-type: direct:production
  update-type: version-update:semver-minor
- dependency-name: org.springdoc:springdoc-openapi-starter-webmvc-ui
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

build.gradle

@@ -19,7 +19,7 @@ ext {
     validationApiVersion = "2.0.1.Final"
     gsonVersion = "2.8.5"
     jwtVersion = "4.4.0"
-    openApiVersion = "2.1.0"
+    openApiVersion = "2.6.0"
     logbookVersion = "2.16.0"
     logstashEncoderVersion = "7.3"
     postgresContainerVersion = "1.19.0"