[chore]: Add integration test coverage for sampling strategy file refresh

[aaryan359]

Requirement

Description

The all-in-one integration test currently verifies that sampling strategies can be retrieved via /api/sampling, but it does not test the runtime refresh of file-based sampling strategies.

Sampling strategy reload is supported in production and covered by unit tests, but the end-to-end behavior in the all-in-one setup is not currently exercised.

There is also an existing TODO in cmd/jaeger/internal/all_in_one_test.go pointing to this gap.

This issue proposes adding integration test coverage to verify that updates to a file-based sampling strategy are detected and served correctly without restarting Jaeger.

[aaryan359]

@yurishkuro @jkowall
I noticed a TODO in the all-in-one integration test related to refreshing the sampling strategy file and opened a PR to address it by adding test coverage.
Please confirm if this is a valid and desired test to have. If not, I’m happy to close the PR and not move forward with it.