Enhance issue handling by adding utils module

Introduce `append_related_issues` function and `IssueRelated` enum to manage related issue linking. Update Gitea action to utilize the new functionality for appending related issues in work package content. Add corresponding tests.

src/gitea/action.rs

@@ -7,6 +7,7 @@ use crate::openproject::user::{GetMe, User};
 use crate::openproject::work::WorkPackageWriter;
 use crate::planning::Issue2WorkActionTrait;
 use url::Url;
+use crate::planning::utils::{append_related_issues, IssueRelated};
 
 pub(crate) struct GiteaAction {}
 
@@ -37,6 +38,9 @@ impl Issue2WorkActionTrait for GiteaAction {
             config.openproject.base_url, args.project_id, work_package.id
         );
 
+        let content = append_related_issues(&IssueRelated::OpenProjectIssue(url.to_string()), &issue.body);
+
+
         println!(
             "new work package created: {:?}, edit at {}",
             work_package.subject, url