Currently, The shrunken target index inherits close to none of the original index's properties.

Since #25035 and #25380, other things are ignored.

At the moment, shrink relies on index templates, and just copies over mappings, and index.analysis.* and index.similarities.* from the original index.

It feels like it would make more sense for the shrunken index to be as close to a copy of the original
as possible. This would mean inheriting all the settings and mappings. Although, it should not inherit the aliases.

One way of solving this is to change the behavior and keep the new behavior behind a backwards-compatible query-param (maybe called copy_existing) that defaults to false.

this flag would be:

• 6.x: log a deprecation warning when using shrink without copy_existing setting explicitly configured to true. Configuring it to false is not allowed.
• 7.0: defaulted to true, still disallowed to be false, and deprecated
• removed in 8.0