[SPARK-51463] Add Spark Connect-generated Swift source code

### What changes were proposed in this pull request?

Like other `Spark Connect` client library, this PR aims to add `Spark Connect`-generated `Swift` source code.
- Connect Client for Python: https://github.com/apache/spark/tree/master/python/pyspark/sql/connect/proto
- Spark Connect Client for Go: https://github.com/apache/spark-connect-go/tree/master/internal/generated

These will be replaced by Swift Plugin later.

### Why are the changes needed?

These files are manually generated from [v4.0.0-rc2](https://github.com/apache/spark/releases/tag/v4.0.0-rc2) tag by the following standard procedures. This will be updated when Apache Spark 4.0.0 is released officially.
```
$ git clone -b v4.0.0-rc2 https://github.com/apache/spark.git
$ cd spark/sql/connect/common/src/main/protobuf/
$ protoc --swift_out=. spark/connect/*.proto
$ protoc --grpc-swift_out=. spark/connect/*.proto

// Remove empty GRPC files
$ git grep 'This file contained no services'
spark/connect/catalog.grpc.swift:// This file contained no services.
spark/connect/commands.grpc.swift:// This file contained no services.
spark/connect/common.grpc.swift:// This file contained no services.
spark/connect/example_plugins.grpc.swift:// This file contained no services.
spark/connect/expressions.grpc.swift:// This file contained no services.
spark/connect/ml.grpc.swift:// This file contained no services.
spark/connect/ml_common.grpc.swift:// This file contained no services.
spark/connect/relations.grpc.swift:// This file contained no services.
spark/connect/types.grpc.swift:// This file contained no services.
```

### Does this PR introduce _any_ user-facing change?

No.

### How was this patch tested?

Pass the CIs.

### Was this patch authored or co-authored using generative AI tooling?

No.

Closes #5 from dongjoon-hyun/SPARK-51463.

Authored-by: Dongjoon Hyun <[email protected]>
Signed-off-by: Dongjoon Hyun <[email protected]>

Author: dongjoon-hyun

.github/.licenserc.yaml

@@ -15,5 +15,6 @@ header:
     - '.asf.yaml'
     - '.nojekyll'
     - 'Package.swift'
+    - '**/*pb.swift'
 
   comment: on-failure