[DOP-31839] Add job tags

[dolfinus]

Change Summary

Mostly a copy-paste of dataset tags:

• Added job_tag table
• Added tags: list field into JobDetailedResponse schema
• Added filter tag_value_id: list[int] into GET /v1/jobs endpoint

Extra changes:

• Renamed table dataset_tags to dataset_tag, as all table names in this repo are singular
• Dropped unused datasets_with_tags fixture
• Replaced dataset_with_tags and create_dataset_with_tags with make_dataset+tag_values fixture

Related issue number

Checklist

• Commit message and PR title is comprehensive
• Keep the change as small as possible
• Unit and integration tests for the changes exist
• Tests pass on CI and coverage does not decrease
• Documentation reflects the changes where applicable
• docs/changelog/next_release/<pull request or issue id>.<change type>.rst file added describing change
  (see CONTRIBUTING.rst for details.)
• My PR is ready to review.

[github-actions]

Coverage Report •

File	Stmts	Miss	Cover	Missing
data_rentgen/db/migrations/versions
2026-01-21_675ed36b7807_add_job_tag.py	9	9	0%	11–12, 15–18, 21–22, 32
2026-01-21_f1c76c422433_rename_table_dataset_tags_to_dataset_tag.py	8	8	0%	11, 14–17, 20–22
data_rentgen/db/repositories
job.py	76	3	96%	183, 207–208
data_rentgen/server/services
dataset.py	27	1	96%	36
job.py	30	1	96%	37
location.py	51	1	98%	58
operation.py	41	1	97%	56
TOTAL	7263	921	87%