Add datastore_data_preview sub-module

[dcgoodwin2112]

Fixes #4672

Describe your changes

Add datastore_data_preview sub-module under modules/datastore/modules/ that renders datastore data as paginated, sortable HTML tables using Drupal core's TableSort and pager. No JavaScript frameworks required.

Integration points:

• #type => 'data_preview' render element
• Block plugin (configurable via Block UI)
• Inline "Preview data" links on dataset edit forms
• Standalone admin page at /admin/dkan/data-preview/{resource_id}
• Preview links on the datastore dashboard

Services:

• dkan.data_preview.resource_resolver — resolves distribution UUIDs or nodes to identifier__version resource IDs
• dkan.data_preview.builder — builds paginated, sortable table render arrays
• dkan.data_preview.datasource.database — direct DB queries to datastore tables
• dkan.data_preview.datasource.api — HTTP queries to DKAN's REST API (supports external sites)

Also includes ArrayDataSource for in-memory data (not a service — instantiate directly).

QA Steps

• Enable module: drush en datastore_data_preview
• Visit /admin/dkan/data-preview/{resource_id} with a valid resource ID — verify paginated sortable table renders
• Click column headers to sort, change page size, navigate pages
• Edit a dataset node — verify "Preview data" links appear next to tabular distributions' download URLs
• Visit /admin/dkan/datastore/status — verify preview links appear for importable resources
• Place the Data Preview Table block via /admin/structure/block — verify it renders with a configured resource ID
• Run phpcs --standard=Drupal,DrupalPractice modules/datastore/modules/datastore_data_preview/ — verify zero errors and warnings
• Run phpunit modules/datastore/modules/datastore_data_preview/tests/ — verify all 112 tests pass

Checklist before requesting review

If any of these are left unchecked, please provide an explanation

• I have updated or added tests to cover my code
• I have updated or added documentation