Expose JsonPatch as public API

[ikhoon]

JsonPatch is only used internally so users can't access it and its subclasses.

centraldogma/common/src/main/java/com/linecorp/centraldogma/internal/jsonpatch/JsonPatch.java

Line 123 in e8ece8f

public final class JsonPatch implements JsonSerializable {

If it is exposed as a public API, users could create JSON patch operations more easily.
For example:

final TextNode emailNode = new TextNode(newEmail);
final JsonPointer jsonPointer = JsonPointer.compile(
        "/user/" + userId + "/email");
final ReplaceOperation replace = new ReplaceOperation(jsonPointer, emailNode);
final JsonNode jsonNode = replace.toJsonNode();
changes.add(Change.ofJsonPatch("/some/path", jsonNode));