Strip azure_blob source + GCP impersonation from v0.51-exaforce

[sundaresanr]

Summary

Parquet-only v0.51-exaforce base. The azure_blob queue source + `src/azure/mod.rs` auth helpers pulled over from v0.45-exaforce used azure-core 0.21 APIs; upstream v0.51 is on 0.25, so those files can't compile without a proper SDK migration. Since neither feature is used in production Vector configs (confirmed: no `type: azure_blob` sources in any chart, no `impersonated_service_account` in any sink config), dropping them is the quickest path to a working v0.51-based `vector-base` image.

Deletions (6 files, ~1490 lines)

• `src/azure/mod.rs`
• `src/internal_events/azure_queue.rs`
• `src/sources/azure_blob/{mod,queue,integration_tests,test}.rs`

Reverts to upstream v0.51 (1e5bc95)

• `src/lib.rs`, `src/internal_events/mod.rs`, `src/sources/mod.rs`
• `src/sinks/azure_blob/{config,integration_tests}.rs`, `src/sinks/azure_common/config.rs`
• `src/gcp.rs`, `src/sinks/gcp/stackdriver/metrics/tests.rs` (drops impersonated_service_account)
• `scripts/environment/{prepare.sh,bootstrap-ubuntu-24.04.sh}`, `scripts/integration/azure/compose.yaml` (cosmetic rebase leftovers)

Kept (parquet codec + fixups)

All the `lib/codecs` parquet pieces, `src/codecs/encoding/config.rs` wiring, `src/sinks/aws_s3/{config,sink}.rs`, `src/sinks/util/encoding.rs` batch encoder trait.

Had to fix issues left over in the merged v0.51-exaforce parquet patches:

• `serializer.rs`: add `Parquet*` to `use super::format::`, fix `Gelf` tuple-vs-unit match, add cfg-guarded `Otlp` arm in `build_batched()`
• `parquet.rs`: drop Rust-2024-illegal `ref mut` in BoolColumnWriter match
• `encoding/mod.rs`: re-export `BatchSerializer`
• `src/codecs/encoding/config.rs`: restore `vector_lib::configurable::configurable_component` (exaforce rebase accidentally dropped it)
• `src/components/validation/resources/mod.rs`: add `Parquet` arm in serializer→deserializer match
• `Cargo.lock`: pin pulsar 6.5.0 → 6.3.1 (exaforce rebase drift; 6.5.0 has new required `ProducerOptions` fields the sink doesn't populate)

Local verification

• `cargo check -p vector` (default features) — green (1m11s)
• `cargo check --tests -p vector --no-default-features --features azure-integration-tests` — green (22.9s)

Both cover the commands the publish workflow runs (`make test-integration-azure` + `make package-aarch64-unknown-linux-gnu-all`).

Downstream

Once merged, the push to `v0.51-exaforce` will trigger `exaforce-publish.yaml` → `vector-base:v0.51-exaforce-` lands in ECR → `operations` repo `goservices/vector_exec_sources/Dockerfile` gets bumped in a separate follow-up PR.

[sundaresanr]

Closing in favor of a cleaner two-PR sequence:

1. Revert PR V0.51 exaforce rebase our changes #31 to restore v0.51-exaforce to pristine upstream-v0.51 state.
2. New PR adding only the parquet codec on top of that — no dead azure_blob / GCP-impersonation code in history, no Cargo.lock drift workaround.

The strip-then-keep approach here worked but leaves ~1500 lines of azure code in v0.51-exaforce history as a "added then deleted" ghost that makes future upstream rebases harder.