chore(config): generate datadog config witness trait

Generate, at build time, a witness trait and fallible driver over the
supported Datadog Agent configuration surface. The generator parses the
generated datadog_configuration.rs and emits, for every key inventoried
as support: full or partial, one consume_<key> method on the
DatadogConfigConsumer trait plus a drive() that calls each method
exactly once. A translator that omits a newly supported key fails to
compile, so the supported surface stays auditable from the schema
overlay.

Add the TranslateError type that drive() surfaces, and the Datadog
source-language normalization metadata (KEY_ALIASES, DatadogRemapper)
used to canonicalize keys before deserialization.

Author: webern

.vale/styles/config/vocabularies/technical/accept.txt

@@ -240,3 +240,9 @@ trivy
 Erlang
 OTP
 respawn(s|ed|ing)?
+typify
+snake_case
+unparsed
+stringify
+cutover
+[Aa]uditability

Cargo.lock

@@ -6,6 +6,7 @@ license = { workspace = true }
 repository = { workspace = true }
 
 [dependencies]
+figment = { workspace = true }
 serde = { workspace = true, features = ["derive"] }
 serde_json = { workspace = true }
 

lib/datadog-agent/config/Cargo.toml

@@ -6,6 +6,8 @@ use datadog_agent_config_overlay_model::{schema_gen, Files, SchemaOverlay};
 mod classifier_gen;
 #[path = "build/datadog_config_gen.rs"]
 mod datadog_config_gen;
+#[path = "build/witness_gen.rs"]
+mod witness_gen;
 
 fn main() {
     let manifest_dir = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
@@ -17,11 +19,14 @@ fn main() {
     println!("cargo:rerun-if-changed=build.rs");
     println!("cargo:rerun-if-changed=build/classifier_gen.rs");
     println!("cargo:rerun-if-changed=build/datadog_config_gen.rs");
+    println!("cargo:rerun-if-changed=build/witness_gen.rs");
 
     let schema_path = files.schema.clone();
     let overlay = SchemaOverlay::load(files).unwrap_or_else(|e| panic!("{e}"));
     let schema_map = schema_gen::load_schema(&schema_path);
 
     classifier_gen::generate(&overlay, &schema_map, &manifest_dir);
     datadog_config_gen::generate(&overlay, &schema_path, &manifest_dir);
+    // Depends on the file datadog_config_gen just wrote: it parses src/datadog_configuration.rs.
+    witness_gen::generate(&overlay, &manifest_dir);
 }