Add support for viewing and creating objectives within an objective in a hierarchy tree

What does this MR do and why?

This MR adds ability to view children Objectives and Key Results within an Objective created under a project, it also allows for creating or adding an existing objective from the hierarchy tree view.

Limitations

The tree view currently doesn't support creating or adding Key Result, it will be added once #381833 (closed) & #385084 (closed) are addressed.

Screenshots or screen recordings

Tree View Empty State	Tree View with Objectives

Objective with Indirect Children	Objective with NO Indirect Children

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Open rails console by running bin/rails console within GDK directory.
2. Enable the feature flag :hierarchy_db_restrictions on a project; Feature.enable(:hierarchy_db_restrictions, Project.find_by_full_path('gitlab-org/gitlab-test')).
3. Enable the feature flag :okrs_mvc on the same project; Feature.enable(:okrs_mvc, Project.find_by_full_path('gitlab-org/gitlab-test')).
4. Visit issues list page for the project by navigating to http://gdk.test:3000/gitlab-org/gitlab-test/-/issues.
5. Create an objective by clicking on dropdown button next to New issue and selecting New objective from the dropdown.
6. Once objective is created, click on it to visit its Work Item page, you should be able to see Tree View below the description.
7. Use Add dropdown button create/add objectives.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related Issues

#381872 (closed)

.gitlab/ci/package-and-test/main.gitlab-ci.yml

@@ -38,23 +38,6 @@ stages:
   extends:
     - .gitlab-qa-install
 
-.omnibus-env:
-  variables:
-    BUILD_ENV: build.env
-  script:
-    - |
-      SECURITY_SOURCES=$([[ ! "$CI_PROJECT_NAMESPACE" =~ ^gitlab-org\/security ]] || echo "true")
-      echo "SECURITY_SOURCES=${SECURITY_SOURCES:-false}" > $BUILD_ENV
-      echo "OMNIBUS_GITLAB_CACHE_UPDATE=${OMNIBUS_GITLAB_CACHE_UPDATE:-false}" >> $BUILD_ENV
-      for version_file in *_VERSION; do echo "$version_file=$(cat $version_file)" >> $BUILD_ENV; done
-      echo "OMNIBUS_GITLAB_RUBY3_BUILD=${OMNIBUS_GITLAB_RUBY3_BUILD:-false}" >> $BUILD_ENV
-      echo "OMNIBUS_GITLAB_CACHE_EDITION=${OMNIBUS_GITLAB_CACHE_EDITION:-GITLAB}" >> $BUILD_ENV
-      echo "Built environment file for omnibus build:"
-      cat $BUILD_ENV
-  artifacts:
-    reports:
-      dotenv: $BUILD_ENV
-
 .update-script:
   script:
     - export QA_COMMAND="bundle exec gitlab-qa Test::Omnibus::UpdateFromPrevious $RELEASE $GITLAB_VERSION $UPDATE_TYPE -- $QA_RSPEC_TAGS $RSPEC_REPORT_OPTS"
@@ -108,9 +91,42 @@ dont-interrupt-me:
 
 trigger-omnibus-env:
   extends:
-    - .omnibus-env
     - .rules:omnibus-build
   stage: .pre
+  needs:
+    # We need this job because we need its `cached-assets-hash.txt` artifact, so that we can pass the assets image tag to the downstream omnibus-gitlab pipeline.
+    - pipeline: $PARENT_PIPELINE_ID
+      job: build-assets-image
+  variables:
+    BUILD_ENV: build.env
+  before_script:
+    - |
+      # This is duplicating the function from `scripts/utils.sh` since `.gitlab/ci/package-and-test/main.gitlab-ci.yml` can be included in other projects.
+      function assets_image_tag() {
+        local cache_assets_hash_file="cached-assets-hash.txt"
+
+        if [[ -n "${CI_COMMIT_TAG}" ]]; then
+          echo -n "${CI_COMMIT_REF_NAME}"
+        elif [[ -f "${cache_assets_hash_file}" ]]; then
+          echo -n "assets-hash-$(cat ${cache_assets_hash_file} | cut -c1-10)"
+        else
+          echo -n "${CI_COMMIT_SHA}"
+        fi
+      }
+  script:
+    - |
+      SECURITY_SOURCES=$([[ ! "$CI_PROJECT_NAMESPACE" =~ ^gitlab-org\/security ]] || echo "true")
+      echo "SECURITY_SOURCES=${SECURITY_SOURCES:-false}" > $BUILD_ENV
+      echo "OMNIBUS_GITLAB_CACHE_UPDATE=${OMNIBUS_GITLAB_CACHE_UPDATE:-false}" >> $BUILD_ENV
+      for version_file in *_VERSION; do echo "$version_file=$(cat $version_file)" >> $BUILD_ENV; done
+      echo "OMNIBUS_GITLAB_RUBY3_BUILD=${OMNIBUS_GITLAB_RUBY3_BUILD:-false}" >> $BUILD_ENV
+      echo "OMNIBUS_GITLAB_CACHE_EDITION=${OMNIBUS_GITLAB_CACHE_EDITION:-GITLAB}" >> $BUILD_ENV
+      echo "GITLAB_ASSETS_TAG=$(assets_image_tag)" >> $BUILD_ENV
+      echo "Built environment file for omnibus build:"
+      cat $BUILD_ENV
+  artifacts:
+    reports:
+      dotenv: $BUILD_ENV
 
 trigger-omnibus:
   extends: .rules:omnibus-build
@@ -128,6 +144,7 @@ trigger-omnibus:
     GITLAB_SHELL_VERSION: $GITLAB_SHELL_VERSION
     GITLAB_WORKHORSE_VERSION: $GITLAB_WORKHORSE_VERSION
     GITLAB_VERSION: $CI_COMMIT_SHA
+    GITLAB_ASSETS_TAG: $GITLAB_ASSETS_TAG
     IMAGE_TAG: $CI_COMMIT_SHA
     TOP_UPSTREAM_SOURCE_PROJECT: $CI_PROJECT_PATH
     SECURITY_SOURCES: $SECURITY_SOURCES