Add support for querying branches and tags in Iceberg

[tdcmeehan]

Iceberg metadata includes branches and tags. The Iceberg connector should have a way of querying these, however, our current time travel implementation (added by #20991) only supports snapshot versions or points in time. We can modify the time travel syntax to also allow the querying of snapshot references, either tags or branches.

Part of #22025

Expected Behavior or Use Case

select * from tab1 FOR SYSTEM_VERSION AS OF 'branch-name'
select * from tab1 FOR SYSTEM_VERSION AS OF 'tag-name'

Presto Component, Service, or Connector

Iceberg connector, with minor changes in parser and SPI to allow String references of tags and branches.

Possible Implementation

Example Screenshots (if appropriate):

Context