out_azure_blob: no workload identity support, though out_azure_kusto has it

`out_azure_kusto` supports `auth_type workload_identity`, but `out_azure_blob` supports only `key` and `sas`.

Both plugins target Azure and are commonly deployed side by side, so this reads as a gap rather than a deliberate difference.

**Request**

`auth_type workload_identity` on `out_azure_blob`, ideally with the same option names as `out_azure_kusto` (`tenant_id`, `client_id`, `workload_identity_token_file`) so configuration stays consistent across the two.

Start by locating the out_azure_blob and out_azure_kusto plugin implementations and comparing their authentication configuration and request setup. Use out_azure_kusto as the reference for tenant_id, client_id, and workload_identity_token_file; done means out_azure_blob accepts auth_type workload_identity with those options while retaining key and sas behavior.

Written by the indexing model from the issue text.