Documentation Update Needed: Outdated Instructions in "Introduction to Plugins"

### Code of Conduct

- [x] I have read and agree to the Insomnia Docs project's [Code of Conduct](https://github.com/Kong/insomnia-docs/blob/main/CODE_OF_CONDUCT.md).

### What article on docs.insomnia.rest is affected?

Introduction to Plugins --> https://docs.insomnia.rest/insomnia/introduction-to-plugins

### What part(s) of the article would you like to see updated?

The section explaining how to install a plugin is outdated. It currently suggests simply entering the plugin name in the Plugins settings, but this no longer works. The following should be added:
1. The users need to enable Allow elevated access for plugins under Preferences > Plugins
2. Add a trusted certificate
3. Add the plugin name to install it, and restart Insomnia if needed.

### Additional information

These changes are in newer versions of insomnia.

### Code of Conduct and Community Expectations

- [x] I agree to follow this project's Code of Conduct
- [x] I agree to abide by the Community Expectations

Open the Introduction to Plugins article at docs.insomnia.rest/insomnia/introduction-to-plugins and locate its plugin-installation section in the documentation source. Update the instructions to cover elevated plugin access, a trusted certificate, entering the plugin name, and restarting Insomnia when needed. Done means the published article matches these steps for newer Insomnia versions.

Written by the indexing model from the issue text.