Replicate owning_cell_id to IAM oauth_clients

What does this MR do and why?

Send owning_cell_id on every OAuth application upsert to IAM, and update the vendored gitlab-iam-grpc gem to IAM 0a44f0f.

IAM oauth_clients gained an owning_cell_id column in gitlab-org/auth/iam!687. IAM needs the value to tell Rails-owned clients (owning_cell_id set) apart from IAM-native dynamic clients (owning_cell_id NULL), so Layer 4 orphan detection only reconciles the clients a cell actually owns. IAM main already requires owning_cell_id >= 1 on upsert, so until this ships, every Rails upsert against that main fails with INVALID_ARGUMENT.

The value sent is Gitlab.config.cell.id.to_i, the same expression AcceptLoginChallengeService already sends to IAM's login-accept RPC. It is not guarded on cell.enabled: replication is a Cells-era mechanism, so an unconfigured cell (id nil, sent as 0) should fail loudly rather than silently replicate ownerless.

References

Related to #629574 (closed).

Precedent: !255329 (merged), !254771 (merged).

Screenshots or screen recordings

N/A, backend-only change.

How to set up and validate locally

1. Enable the flag: Feature.enable(:iam_data_replication)
2. Create or update an Authn::OauthApplication and let it replicate (or drive Authn::IamReplication::OauthApplicationReplicator#deliver directly)
3. Confirm the upsert request IAM receives carries owning_cell_id equal to Gitlab.config.cell.id

In case you want to test E2E: !249860 (merged)

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