Merged PR 1557887: Change error file mapping name

### Does this PR have any customer impact?
No
### Type (Feature, Refactoring, Bugfix, DevOps, Testing, Perf, etc)
Refactor
### Does it involve schema level changes? (Table, Column, Index, UDF, etc level changes)
No
### Are you introducing any new config? If yes, do you have tests with and without them being set?
No
### Release Note (Refer [Template](../docs/release_notes/pgmongo_template.md))

### Description
Rename error file mapping

----
#### AI description  (iteration 1)
#### PR Classification
Code cleanup

#### PR Summary
This pull request updates the name of the error mapping file and adjusts references accordingly.
- `Makefile`: Updated references from `mongoerrors.csv` to `error_mappings.csv`.
- `docs/pgmongo/design_docs/data_plane/backend_common/error_management.md`: Updated documentation to reflect the new file name.
- `src/utils/documentdb_conversion_codes.c`: Updated comment to reference the new file name.
- Moved `oss/mongoerrors.csv` to `oss/error_mappings.csv` without code changes.

Author: visridha

mongoerrors.csv error_mappings.csvmongoerrors.csv renamed to error_mappings.csv

@@ -1,4 +1,4 @@
-MongoError,ErrorName
+ErrorMapping,ErrorName
 1,InternalError
 2,BadValue
 5,GraphContainsCycle