feat(axiom sink): Add regional edge support for data ingestion

Adds a new optional `region` configuration field to the axiom sink that
allows users to specify a regional edge URL for data ingestion. When
configured, data is sent to the regional edge endpoint instead of the
default cloud endpoint.

This enables:
- Improved data locality and regional compliance
- Support for both production (axiom.co) and testing (e.g., axiomtestlabs.co) domains
- Backward compatibility - existing configurations continue to work unchanged

Example configuration:
```yaml
[sinks.axiom]
type = "axiom"
token = "${AXIOM_TOKEN}"
dataset = "my-dataset"
region = "https://eu-central-1.aws.edge.axiom.co"
```

The implementation uses the new edge endpoint format:
`{region}/v1/ingest/{dataset}` when region is set, otherwise falls back
to the existing cloud endpoint format:
`{url}/v1/datasets/{dataset}/ingest`

Author: toppercodes

changelog.d/axiom_regional_edges.feature.md

@@ -0,0 +1,3 @@
+The `axiom` sink now supports regional edges for data locality. A new optional `region` configuration field allows you to specify the full regional edge URL (e.g., `https://eu-central-1.aws.edge.axiom.co`, `https://us-east-1.aws.edge.axiom.co`). When configured, data is sent to the regional edge endpoint instead of the default cloud endpoint.
+
+authors: toppercodes

src/sinks/axiom.rs

@@ -30,6 +30,7 @@ pub struct AxiomConfig {
     /// URI of the Axiom endpoint to send data to.
     ///
     /// Only required if not using Axiom Cloud.
+    /// Note: This is ignored if `region` is set.
     #[configurable(validation(format = "uri"))]
     #[configurable(metadata(docs::examples = "https://axiom.my-domain.com"))]
     #[configurable(metadata(docs::examples = "${AXIOM_URL}"))]
@@ -52,6 +53,15 @@ pub struct AxiomConfig {
     #[configurable(metadata(docs::examples = "vector_rocks"))]
     dataset: String,
 
+    /// The Axiom regional edge URL to use for ingestion.
+    ///
+    /// When set, data will be sent to the regional edge endpoint instead of the default cloud endpoint.
+    #[configurable(validation(format = "uri"))]
+    #[configurable(metadata(docs::examples = "${AXIOM_REGION}"))]
+    #[configurable(metadata(docs::examples = "https://eu-central-1.aws.edge.axiom.co"))]
+    #[configurable(metadata(docs::examples = "https://us-east-1.aws.edge.axiom.co"))]
+    region: Option<String>,
+
     #[configurable(derived)]
     #[serde(default)]
     request: RequestConfig,
@@ -150,6 +160,11 @@ impl SinkConfig for AxiomConfig {
 
 impl AxiomConfig {
     fn build_endpoint(&self) -> String {
+        if let Some(region_url) = &self.region {
+            let region_url = region_url.trim_end_matches('/');
+            return format!("{}/v1/ingest/{}", region_url, self.dataset);
+        }
+
         let url = if let Some(url) = self.url.as_ref() {
             url.clone()
         } else {
@@ -182,6 +197,63 @@ mod test {
             "https://axiom.my-domain.com/v1/datasets/vector_rocks/ingest"
         );
     }
+
+    #[test]
+    fn test_regional_edge_endpoint() {
+        let config = super::AxiomConfig {
+            region: Some("https://eu-central-1.aws.edge.axiom.co".to_string()),
+            dataset: "vector_rocks".to_string(),
+            ..Default::default()
+        };
+        let endpoint = config.build_endpoint();
+        assert_eq!(
+            endpoint,
+            "https://eu-central-1.aws.edge.axiom.co/v1/ingest/vector_rocks"
+        );
+
+        // Test with trailing slash in region URL
+        let config = super::AxiomConfig {
+            region: Some("https://us-east-1.aws.edge.axiom.co/".to_string()),
+            dataset: "my-dataset".to_string(),
+            ..Default::default()
+        };
+        let endpoint = config.build_endpoint();
+        assert_eq!(
+            endpoint,
+            "https://us-east-1.aws.edge.axiom.co/v1/ingest/my-dataset"
+        );
+    }
+
+    #[test]
+    fn test_regional_edge_with_custom_domain() {
+        // Regional edge with custom domain (e.g., testing environment)
+        let config = super::AxiomConfig {
+            region: Some("https://eu-central-1.aws.edge.axiomtestlabs.co".to_string()),
+            dataset: "test-dataset".to_string(),
+            ..Default::default()
+        };
+        let endpoint = config.build_endpoint();
+        assert_eq!(
+            endpoint,
+            "https://eu-central-1.aws.edge.axiomtestlabs.co/v1/ingest/test-dataset"
+        );
+    }
+
+    #[test]
+    fn test_region_takes_precedence() {
+        // When both region and url are set, region takes precedence
+        let config = super::AxiomConfig {
+            url: Some("https://api.axiom.co".to_string()),
+            region: Some("https://us-west-1.aws.edge.axiom.co".to_string()),
+            dataset: "my-dataset".to_string(),
+            ..Default::default()
+        };
+        let endpoint = config.build_endpoint();
+        assert_eq!(
+            endpoint,
+            "https://us-west-1.aws.edge.axiom.co/v1/ingest/my-dataset"
+        );
+    }
 }
 
 #[cfg(feature = "axiom-integration-tests")]