[WEB-4999] feat: implement flexible data export utility with CSV, JSON, and XLSX support (#7884)

* feat: implement flexible data export utility with CSV, JSON, and XLSX support

- Introduced Exporter class for handling various data formats.
- Added formatters for CSV, JSON, and XLSX exports.
- Created schemas for defining export fields and their transformations.
- Implemented IssueExportSchema for exporting issue data with nested attributes.
- Enhanced issue export task to utilize the new exporter system for better data handling.

* feat: enhance issue export functionality with new relations and context handling

- Updated issue export task to utilize new IssueRelation model for better relationship management.
- Refactored Exporter class to accept QuerySets directly, improving performance and flexibility.
- Enhanced IssueExportSchema to include parent issues and relations in the export.
- Improved documentation for exporting multiple projects and filtering fields during export.

* feat: enhance export functionality with field filtering and context support

- Updated Exporter class to merge fields into options for formatting.
- Modified formatters to filter fields based on specified options.
- Enhanced ExportSchema to support optional field selection during serialization.
- Improved documentation for the serialize method to clarify field filtering capabilities.

* fixed type

Author: dheeru0198

apps/api/plane/bgtasks/export_task.py

@@ -273,6 +273,21 @@ class IssueRelationChoices(models.TextChoices):
     IMPLEMENTED_BY = "implemented_by", "Implemented By"
 
 
+# Bidirectional relation pairs: (forward, reverse)
+# Defined after class to avoid enum metaclass conflicts
+IssueRelationChoices._RELATION_PAIRS = (
+    ("blocked_by", "blocking"),
+    ("relates_to", "relates_to"),  # symmetric
+    ("duplicate", "duplicate"),  # symmetric
+    ("start_before", "start_after"),
+    ("finish_before", "finish_after"),
+    ("implemented_by", "implements"),
+)
+
+# Generate reverse mapping from pairs
+IssueRelationChoices._REVERSE_MAPPING = {forward: reverse for forward, reverse in IssueRelationChoices._RELATION_PAIRS}
+
+
 class IssueRelation(ProjectBaseModel):
     issue = models.ForeignKey(Issue, related_name="issue_relation", on_delete=models.CASCADE)
     related_issue = models.ForeignKey(Issue, related_name="issue_related", on_delete=models.CASCADE)