Remove ExtraMetadata in favor of SparseFields

[Copilot]

ExtraMetadata was a stopgap for storing custom per-resource metadata. With the metadata JSON schema system and SparseField now available, ExtraMetadata is superseded and can be removed.

Migration

A single migration (0098) handles both data and schema changes:

• Data: Each ExtraMetadata row is migrated to a SparseField entry with name=extra_metadata_<pk> and value=json.dumps(metadata_dict). Entries whose serialized JSON exceeds the 1024-char SparseField.value limit are skipped with a warning.
• Schema: Removes the metadata M2M field from ResourceBase and drops the ExtraMetadata model.

Code removal

• base/models.py: Removed ExtraMetadata model and ResourceBase.metadata M2M field.
• base/api/serializers.py: Removed ExtraMetadataSerializer and metadata deferred field from ResourceBaseSerializer.
• base/api/views.py: Removed extra_metadata REST action (GET/PUT/POST/DELETE on /{pk}/extra_metadata/).
• base/utils.py: Removed validate_extra_metadata() and its schema/settings imports.
• resource/utils.py / resource/manager.py: Removed extra_metadata parameter from update_resource() and ResourceManager.update().
• api/resourcebase_api.py: Removed metadata__* query param filtering from the legacy Tastypie API.
• settings.py: Removed DEFAULT_EXTRA_METADATA_SCHEMA, CUSTOM_METADATA_SCHEMA, EXTRA_METADATA_SCHEMA, and from schema import Optional.

Tests

Removed TestExtraMetadataBaseApi and all test_extra_metadata_included_with_param / test_metadata_filters tests that covered the now-deleted functionality.

Note for external API consumers: The /extra_metadata/ endpoint and the metadata field in resource API responses are gone. Use the sparse fields API instead.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Refact extraMetadata</issue_title>
<issue_description>The extraMetadata field was introduced in order to store custom metadata without modifying the model.
After the introduction of the new metadata json schema and the possibility to access the sparse metadata fields, the extraMetadata field becomes outdated.

External clients (if any) using the API for handling the extraMetadata should be updated to use the new sparse field API.

So, at least, we need:

• migration to move extraMetadata content into sparse fields
• extraMetadatata field removal + related migration

IF we want to maintain back compatibility, we need to make sure that read and write accesses for the extraMetadata still work:

• refact the views that handle extraMetadata field as input, and store the inner properties in SparseFields
• refact the serializers outputting the extraMetadata, making them read the sparsefields instead.

@giohappy These last two points needs discussion to find out if they are really needed.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Refact extraMetadata #14000

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[etj]

@copilot format with back, checks are failing because of it

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[Copilot]

@copilot format with back, checks are failing because of it

Fixed in cfc914c. The flake8 errors were:

• QuerySet imported but unused in serializers.py (was only used by the removed ExtraMetadataSerializer)
• IsOwnerOrAdmin imported but unused in views.py (was only used by the removed extra_metadata action)
• Trailing blank line at end of models.py
• urljoin imported but unused in geoapps/api/tests.py (was only used by the removed test method)