fix(web-console): avoid schema discovery for Druid reingestion

[sakshichitnis27]

Fixes #19036.

Description

The classic batch loader currently enables schema discovery while sampling Druid input sources. Complex metric values returned during reingestion are then treated as dimensions, causing the sampler to fail with Unhandled type: COMPLEX.

This PR disables schema discovery only for Druid reingestion samples, restoring the behavior from before the Delta sampling change. Other fixed-format sources, including Delta, continue to use schema discovery.

Regression tests cover both request shapes.

Release note

Fixed classic batch loader sampling when reingesting from Druid datasources that contain complex metrics.

Testing

• npx jest --config jest.config.js src/utils/sampler.spec.ts --runInBand
• npx jest --config jest.config.js --testPathIgnorePatterns=e2e-tests --runInBand (167 suites, 852 tests)
• npm run typecheck
• npm run eslint
• npm run sasslint
• npm run prettify-check

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Key changed/added classes in this PR

• sampleForConnect

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This PR has:

• been self-reviewed.
• a release note entry in the PR description.
• added unit tests to cover the changed code paths.