feat[sdk] add service account helper

[harksin]

Note

Service account authentication support

• Adds sdk/service_account.go with ServiceAccount, loaders (LoadServiceAccount, LoadServiceAccountFromJSON/Reader), validation, issuer parsing, ServiceAccountOptions, and ToConfiguration
• Adds client constructors in sdk/client.go: NewClientFromServiceAccount, NewClientFromServiceAccountFile, NewClientFromServiceAccountJSON
• Adds defaults/utilities in sdk/utils/helpers.go: DefaultRequestTimeout, DefaultMaxRetries, SecondsToDuration

Tests and examples

• New sdk/service_account_test.go covering JSON loading, issuer parsing, config conversion, and client construction
• Updates sdk/builders/fluent/query_test.go to use DataDockID and adjust expected path
• Adds usage_examples/service_account_examples.go demonstrating file/JSON-based setup and dev TLS skipping

Tooling

• run_tests.sh: run unit tests across all ./sdk/... packages

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[martinmdj]

LGTM, maybe we could avoid mentionning keycloak and centering the sdk around keycloak. This could be relevant if we ever move away from it / support more idps.