Support Change Streams DDL

[apstndb]

Support DDLs for managing change streams.

https://cloud.google.com/spanner/docs/change-streams/manage?hl=en

• CREATE CHANGE STREAM <name> FOR ...
• ALTER CHANGE STREAM <name> SET FOR ...
• ALTER CHANGE STREAM <name> SET OPTIONS ...
• ALTER CHANGE STREAM <name> DROP FOR ALL
• DROP CHANGE STREAM <name>

spanner> CREATE CHANGE STREAM EverythingStream FOR ALL;
ERROR: invalid statement

I propose to support generic CREATE / DROP / ALTER DDL statements so that spanner-cli can respond to the new features of Cloud Spanner with a minimum of effort.

[yfuruyama]

Sounds good 👍

We can also think about providing List Change Streams with the syntax like SHOW CHANGE STREAMS, but it can be discussed later once we support the above essential DDL.