Allow modification of built-in extension data

[ruibaby]

Prerequisites

• I have searched for related issues in the Issues list.
• This is a feature related to Halo. If it is not an issue with the project itself, it is recommended to submit it in the Discussions.
• If it is a feature suggestion for plugins and themes, please submit it in the respective plugin and theme repositories.

Your current Halo version

2.21.9

Describe this feature

The system ships with some built-in data, such as the default attachment storage policy and user role definitions. However, this data can't be modified from the admin panel because any changes are reverted on the next restart.

This mechanism can be quite inconvenient in common use cases. For example:

1. If I want to modify the default storage policy to only allow image uploads, my only option is to create a new policy instead of editing the default one.
2. If I want to add more permissions to a built-in role, I have to create a new custom role from scratch.

/area core
/milestone 2.22.x

Additional information

No response