[Feature][MTMV] Support modifying `replication_allocation` property for Async Materialized View (MTMV)

[cheungfeifu]

Search prior failures

• I have searched the existing issues and found no similar proposal.

Is your feature request related to a problem? Please describe.

Currently, when creating an Async Materialized View (MTMV) in Doris, the physical table associated with the MTMV inherits the replication_allocation property from the base tables or falls back to global default configurations.

However, in production scenarios with multi-tag BE clusters (e.g., hot/cold data isolation, default vs. offline tags), users often need to alter the replica allocation of existing Async Materialized Views (e.g., moving MTMV replicas to dedicated offline BE nodes to isolate query workloads).

Currently, attempting to modify the replication_allocation for an existing MTMV via SQL either lacks dedicated DDL syntax or fails to propagate the property change down to the underlying partitions/table correctly.

Describe the solution you'd like

1. Syntax Support:
   Support altering the replication_allocation property for Async Materialized Views using DDL, for example:

   ALTER MATERIALIZED VIEW [db_name.]mv_name SET ("replication_allocation" = "tag.location.default: 1, tag.location.offline: 2");