Support named PLACEMENT POLICY

[morgo]

This is a sub-task of Placement Rules in SQL: #18030

Support the ability to CREATE PLACEMENT POLICY with the same options available in CREATE TABLE|ALTER TABLE context.

The following subtasks are known:

• Parser: {CREATE|ALTER} PLACEMENT POLICY placement_options parser: support create and alter placement policy parser#1313
• Parser: SHOW CREATE PLACEMENT POLICY x, DROP PLACEMENT POLICY [IF EXISTS] x; parser: support drop placement policy parser#1295 parser: support show create placement policy parser#1298
• Design table in mysql.* for persisting placement policies. meta: support storing placement policy into meta #27251
• Ensure {CREATE|ALTER|DROP} PLACEMENT POLICY requires the PLACEMENT_ADMIN privilege Ensure {CREATE|ALTER|DROP} PLACEMENT POLICY requires the PLACEMENT_ADMIN privilege #27603
• Support ALTER PLACEMENT POLICY #27714
• ALTER PLACEMENT POLICY should update placement rules for all tables in scope in PD.
• DROP PLACEMENT POLICY should clear the placement rules for all tables in scope in PD, and reset the SHOW CREATE TABLE info to no longer have the placement policy named.

[morgo]

I have moved the tasks of this sub-issue to #18030

This was a suggestion to make it easier to see what tasks are unassigned. It makes sense to me, so I am going to close this issue.