Summary:
UpgradeYsql can be invoked by the user via the yb-admin `upgrade_ysql` command. If the user calls this on a universe without ysql, then we should early exist the function.

Fixes #27167
Jira: DB-16653

Original commit: e210cdfc027cccda6a3facbfb751736535fb8d42 / D45096

Test Plan: TEST_F(YcqlOnlyUpgradeTest, TestUpgrade) {

Reviewers: telgersma, smishra

Reviewed By: smishra

Subscribers: ybase

Differential Revision: https://phorge.dev.yugabyte.com/D45128