Add .enrich exemption to DotPrefixValidator

[juretratnjek]

Elasticsearch Version

8.18.2

Installed Plugins

No response

Java Version

bundled

OS Version

not related to operating system

Problem Description

Hi team.

While preparing for an upgrade to 9.0.5 from 8.18.2, there is a warning shown as deprecation:
Warning - Index [.enrich-calculated_enrich_policy-1758322200400] name begins with a dot (.), which is deprecated, and will not be allowed in a future Elasticsearch version.

As stated in documentation for enrich policies, .enrich* indices are system indices and an exception should be added to DotPrefixValidator for these indices:

Enrich indices contain enrich data from source indices but have a few special properties to help streamline them:

They are system indices, meaning they’re managed internally by Elasticsearch and only intended for use with enrich processors and the ES|QL ENRICH command.

They` always begin with .enrich-*.

Steps to Reproduce

Warning is written to deprecation logs.

Logs (if relevant)

No response

[elasticsearchmachine]

Pinging @elastic/es-data-management (Team:Data Management)

[dakrone]

This would be fixed by #128868 which is a better way, rather than adding this as an exemption.