Add DGA domain object template with algorithm context

[adulau]

Motivation

• Provide a dedicated MISP object to model Domain Generation Algorithm (DGA) outputs and capture generation context to improve sharing and detection of DGA-based infrastructure.
• Close the referenced issue by adding explicit fields for algorithm metadata, seed/epoch/counter, TLD strategy, validity window and malware family, with the USENIX paper as a reference.

Description

• Add a new object template at objects/dga-domain/definition.json named dga-domain that models generated domains and algorithm context and sets requiredOneOf to domain or algorithm-name.
• The new object exposes attributes including algorithm-name, algorithm-version, seed, epoch, counter, tld, domain, malware-family, validity-start, validity-end, reference and text for analyst notes.
• Document the new object by adding its entry to README.md with a link to the object definition and the USENIX reference paper.

Testing

• Ran ./jq_all_the_things.sh to normalize JSON formatting and reserialize templates (completed, but the environment emitted uuidparse warnings because the uuidparse utility is not installed).
• Validated JSON syntax with jq using jq . objects/dga-domain/definition.json which succeeded.
• Checked UUID uniqueness with python3 unique_uuid.py, which produced no conflicts.
• Schema validation with jsonschema -i objects/dga-domain/definition.json schema_objects.json could not be executed because the jsonschema binary is not available in this environment.

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Codex Task