chore: add schema id

[Vessel9817]

Description

Following the addition to SchemaStore via SchemaStore/schemastore#5986, the Trivy config schema should have a unique ID. From the draft-2020-12 spec:

Note that this URI is an identifier and not necessarily a network locator. In the case of a network-addressable URL, a schema need not be downloadable from its canonical URI.

If present, the value for this keyword MUST be a string, and MUST represent a valid URI-reference [RFC3986]. This URI-reference SHOULD be normalized, and MUST resolve to an absolute-URI [RFC3986] (without a fragment), or to a URI with an empty fragment.

The provided ID is one such example of a URI following this spec. If, for whatever reason, SchemaStore/schemastore#5986 isn't merged, the ID can be changed to, for instance, https://raw.githubusercontent.com/aquasecurity/trivy/main/schema/trivy-config.json. Although the spec dictates that the schema need not be downloadable from its ID, this quality does avoid confusion.

Checklist

• I've read the guidelines for contributing to this repository.
• I've followed the conventions in the PR title.
• I've added tests that prove my fix is effective or that my feature works.
• I've updated the documentation with the relevant information (if needed).
• I've added usage information (if the PR introduces new options)
• I've included a "before" and "after" example to the description (if the PR is a user interface change).

[CLAassistant]

All committers have signed the CLA.

[DmitriyLewen]

We generate this file using generateConfigSchema() (in mage package).
You need to update this function.

[DmitriyLewen]

Because this PR hasn't been merged yet, I think we can wait a bit.
If they don't merge it, we'll change the URL to https://raw.githubusercontent.com/aquasecurity/trivy/main/schema/trivy-config.json.

[Vessel9817]

It's just been merged, should be up on the website later