feat: add apis for Mutation and RowMutationEntry (#1454)

* feat: add apis for Mutation and RowMutationEntry

* use iterable instead of iterator

* 🦉 Updates from OwlBot post-processor

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Author: mutianf

google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/data/v2/models/Mutation.java

@@ -87,6 +87,19 @@ public static Mutation fromProtoUnsafe(List<com.google.bigtable.v2.Mutation> pro
     return mutation;
   }
 
+  /**
+   * Wraps the List of protobuf {@link com.google.bigtable.v2.Mutation}. This methods, like {@link
+   * #createUnsafe()}, allows setCell operation to use server side timestamp. This is dangerous
+   * because mutations will no longer be idempotent, which might cause multiple duplicate values to
+   * be stored in Bigtable. This option should only be used for advanced usecases with extreme care.
+   */
+  @BetaApi
+  public static Mutation fromProtoUnsafe(Iterable<com.google.bigtable.v2.Mutation> protos) {
+    Mutation mutation = new Mutation(true);
+    mutation.mutations.addAll(protos);
+    return mutation;
+  }
+
   /**
    * Constructs a row mutation from an existing protobuf object.
    *

google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/data/v2/models/RowMutationEntry.java

@@ -15,6 +15,7 @@
  */
 package com.google.cloud.bigtable.data.v2.models;
 
+import com.google.api.core.BetaApi;
 import com.google.api.core.InternalApi;
 import com.google.bigtable.v2.MutateRowsRequest;
 import com.google.common.base.Preconditions;
@@ -54,6 +55,13 @@ public static RowMutationEntry create(@Nonnull ByteString key) {
     return new RowMutationEntry(key, Mutation.create());
   }
 
+  /** Creates a new instance from existing mutation. */
+  @BetaApi
+  public static RowMutationEntry createFromMutationUnsafe(
+      @Nonnull ByteString key, @Nonnull Mutation mutation) {
+    return new RowMutationEntry(key, mutation);
+  }
+
   /**
    * Creates new instance of mutation builder which allows server timestamp for setCell operations.
    *