tree wide: clippy lint fixes

most (not all) where done automatically

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

pbs-config/src/prune.rs

@@ -35,7 +35,7 @@ pub fn lock_config() -> Result<BackupLockGuard, Error> {
 
 pub fn config() -> Result<(SectionConfigData, [u8; 32]), Error> {
     let content = proxmox_sys::fs::file_read_optional_string(PRUNE_CFG_FILENAME)?;
-    let content = content.unwrap_or_else(String::new);
+    let content = content.unwrap_or_default();
 
     let digest = openssl::sha::sha256(content.as_bytes());
     let data = CONFIG.parse(PRUNE_CFG_FILENAME, &content)?;