Auto merge of #14683 - dacianpascu06:355adcad7, r=epage

Added unstable-schema generation for Cargo.toml

### What does this PR try to resolve?

Added unstable-schema feature that generates JsonSchema for Cargo.toml

See #12883
finished first step of [plan](#12883 (comment))

### Information
In cargo-util-schemas,  run cargo test --feature unstable-schema  . If there have been any changes to manifest.schema.json, rerun with env variable SNAPSHOTS=overwrite  and it will update them.

### How should we test and review this PR?
In cargo-util-schemas run cargo test --features unstable-schema and it will generate manifest.schema.json

Author: bors

Cargo.lock

@@ -83,6 +83,7 @@ rusqlite = { version = "0.32.0", features = ["bundled"] }
 rustc-hash = "2.0.0"
 rustfix = { version = "0.8.2", path = "crates/rustfix" }
 same-file = "1.0.6"
+schemars = "0.8.21"
 security-framework = "2.11.1"
 semver = { version = "1.0.23", features = ["serde"] }
 serde = "1.0.204"

Cargo.toml

@@ -9,8 +9,10 @@ repository.workspace = true
 description = "Deserialization schemas for Cargo"
 
 [dependencies]
+schemars = { workspace = true, features = ["preserve_order","semver"], optional = true }
 semver.workspace = true
 serde = { workspace = true, features = ["derive"] }
+serde_json = { workspace = true, optional = true }
 serde-untagged.workspace = true
 serde-value.workspace = true
 thiserror.workspace = true
@@ -23,3 +25,6 @@ workspace = true
 
 [dev-dependencies]
 snapbox.workspace = true
+
+[features]
+unstable-schema = ["dep:schemars", "dep:serde_json"]