Fix missing order by fields in SELECT statement

[antisaling]

Currently, it's not possible to order by creation time or update time when using a MySQL backend. The PostgresQL backend also won't allow ordering by update time.

All such queries fail with (e.g. on MySQL):

rpc error: code = Internal desc = mysql_query failed: errno: Expression #1 of ORDER BY clause is not in SELECT list, references column 'model_registry.table_0.create_time_since_epoch' which is not in SELECT list; this is incompatible with DISTINCT, error: Expression #1 of ORDER BY clause is not in SELECT list, references column 'model_registry.table_0.create_time_since_epoch' which is not in SELECT list; this is incompatible with DISTINCT

Description

Fixes missing order by fields in SELECT statement.

Fixes: kubeflow/model-registry#358

How Has This Been Tested?

See opendatahub-io#12.

Merge criteria:

• The commits are squashed in a cohesive manner and have meaningful messages.
• Testing instructions have been added in the PR body (for PRs involving changes that are not immediately obvious).
• The developer has manually tested the changes and verified that the changes work

[antisaling]

@XinranTang hi, could you take a look?

[chensun]

Overall LGTM. But I'll defer to MLMD owner for the formal review.

nit: Can you add some unit tests for the change? It seems there're adjacent test file: ml_metadata/metadata_store/postgresql_query_executor_test.cc