feat(templates): add EntityDef and entity-driven orchestration to Sql…

[AtMrun]

…MetadataExtractor

Introduces declarative entity definitions that replace hardcoded asyncio.gather of 4 entities in SqlMetadataExtractor.run().

• EntityDef dataclass: name, sql, endpoint, phase, enabled, timeout
• Phased orchestration: entities grouped by phase, run concurrently within phase, sequentially across phases
• fetch_entity() dispatches to fetch{name}() methods by convention
• Full backward compat: empty entities list falls back to default 4 (databases, schemas, tables, columns)
• Adding a new entity type is one line in the entities list

What a Snowflake extractor looks like:

class SnowflakeExtractor(SqlMetadataExtractor):
    entities = [
        EntityDef(name="databases", phase=1),
        EntityDef(name="schemas",   phase=1),
        EntityDef(name="stages",    phase=2),
        EntityDef(name="streams",   phase=2),
    ]

Changelog

• to be added

Additional context (e.g. screenshots, logs, links)

• to be added

Checklist

• Additional tests added
• All CI checks passed
• Relevant documentation updated

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Copyleft License Compliance

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[snykgituser]

✅ Snyk checks have passed. No issues have been found so far.

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[Aryamanz29]

Closing — duplicate of #1298 (same feature, earlier iteration). Branch preserved.