[C++] Expose ZSTD and Snappy compression to C API (apache#7014)

### Motivation

I'd like to be able to use zstd and/or Snappy compression with the C API, so I've added them to the `pulsar_compression_type` enum.

### Modifications

I've added `pulsar_CompressionZSTD` and `pulsar_CompressionSNAPPY` to `pulsar_compression_type`

pulsar-client-cpp/include/pulsar/c/producer_configuration.h

@@ -39,7 +39,9 @@ typedef enum { pulsar_Murmur3_32Hash, pulsar_BoostHash, pulsar_JavaStringHash }
 typedef enum {
     pulsar_CompressionNone = 0,
     pulsar_CompressionLZ4 = 1,
-    pulsar_CompressionZLib = 2
+    pulsar_CompressionZLib = 2,
+    pulsar_CompressionZSTD = 3,
+    pulsar_CompressionSNAPPY = 4
 } pulsar_compression_type;
 
 typedef enum {