kms: add context.Context to KMS API calls (#15327)

This commit adds a `context.Context` to the
the KMS `{Stat, CreateKey, GenerateKey}` API
calls.

The context will be used to terminate external calls
as soon as the client requests gets canceled.

A follow-up PR will add a `context.Context` to
the remaining `DecryptKey` API call.

Signed-off-by: Andreas Auernhammer <hi@aead.dev>

cmd/format-disk-cache.go

@@ -359,7 +359,7 @@ func migrateCacheData(ctx context.Context, c *diskCache, bucket, object, oldfile
 
 	actualSize := uint64(st.Size())
 	if globalCacheKMS != nil {
-		reader, err = newCacheEncryptReader(readCloser, bucket, object, metadata)
+		reader, err = newCacheEncryptReader(ctx, readCloser, bucket, object, metadata)
 		if err != nil {
 			return err
 		}