api types/config: add sync-push config type for push sync jobs

In order for sync jobs to be either pull or push jobs, allow to
configure the direction of the job.

Adds an additional config type `sync-push` to the sync job config, to
clearly distinguish sync jobs configured in pull and in push
direction and defines and implements the required `SyncDirection` api
type.

This approach was chosen in order to limit possible misconfiguration,
as unintentionally switching the sync direction could potentially
delete still required snapshots.

Signed-off-by: Christian Ebner <c.ebner@proxmox.com>

pbs-api-types/src/jobs.rs

@@ -498,6 +498,44 @@ pub const TRANSFER_LAST_SCHEMA: Schema =
         .minimum(1)
         .schema();
 
+#[api()]
+#[derive(Copy, Clone, Debug, Default, Eq, PartialEq, Serialize, Deserialize)]
+#[serde(rename_all = "kebab-case")]
+/// Direction of the sync job, push or pull
+pub enum SyncDirection {
+    /// Sync direction pull
+    #[default]
+    Pull,
+    /// Sync direction push
+    Push,
+}
+
+impl std::fmt::Display for SyncDirection {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            SyncDirection::Pull => f.write_str("pull"),
+            SyncDirection::Push => f.write_str("push"),
+        }
+    }
+}
+
+impl SyncDirection {
+    pub fn as_config_type_str(&self) -> &'static str {
+        match self {
+            SyncDirection::Pull => "sync",
+            SyncDirection::Push => "sync-push",
+        }
+    }
+
+    pub fn from_config_type_str(config_type: &str) -> Result<Self, anyhow::Error> {
+        match config_type {
+            "sync" => Ok(SyncDirection::Pull),
+            "sync-push" => Ok(SyncDirection::Push),
+            _ => bail!("invalid config type for sync job"),
+        }
+    }
+}
+
 #[api(
     properties: {
         id: {