add: hizsearch plugin

[hiz0147]

HizSearch-Millennium

Adds HizSteamButton as a Millennium plugin.
Extensively tested and approved by the community (over 335 stars on GitHub); now includes the option to install with Millenium.

Repository: https://github.com/hiz0147/HizSearch-Millennium

Task Checklist

Developer

• I am the original author or an authorized maintainer of this plugin.
• I have complied with all license requirements for the libraries used, including providing appropriate notices where necessary.
• My plugin is fully open source and does not depend on any external paid services, except for widely trusted and well-known platforms. Additionally, neither I nor anyone associated with me profits from any such services.

Plugin Functionality

• I have tested the plugin on both the Stable and Beta Steam update channels.
• My plugin is unique, or provides additional or alternative functionality to plugins already on the store.

Testing Instructions

• Verified by a third party on Steam Client Stable.
• Verified by a third party on Steam Client Beta.