cloud_storage: add upload_manifest with path arg

I have some upcoming changes that move ownership of deciding a path to a
centralized location. To that end, the cloud_storage::remote will have
less ssay in the path names of manifests.

This commit is a small foundational change to expose an upload_manifest
call in which callers can determine the path. Later changes will begin
using this more extensively, and eventually the call where remote picks
a name will be removed.

src/v/cloud_storage/remote.cc

@@ -365,11 +365,19 @@ ss::future<download_result> remote::do_download_manifest(
 ss::future<upload_result> remote::upload_manifest(
   const cloud_storage_clients::bucket_name& bucket,
   const base_manifest& manifest,
+  retry_chain_node& parent) {
+    auto key = manifest.get_manifest_path();
+    co_return co_await upload_manifest(bucket, manifest, key, parent);
+}
+
+ss::future<upload_result> remote::upload_manifest(
+  const cloud_storage_clients::bucket_name& bucket,
+  const base_manifest& manifest,
+  const remote_manifest_path& key,
   retry_chain_node& parent) {
     auto guard = _gate.hold();
     retry_chain_node fib(&parent);
     retry_chain_logger ctxlog(cst_log, fib);
-    auto key = manifest.get_manifest_path();
     auto path = cloud_storage_clients::object_key(key());
     auto lease = co_await _pool.local().acquire(fib.root_abort_source());
     auto permit = fib.retry();

src/v/cloud_storage/remote.h

@@ -291,6 +291,12 @@ class remote
       const base_manifest& manifest,
       retry_chain_node& parent);
 
+    ss::future<upload_result> upload_manifest(
+      const cloud_storage_clients::bucket_name& bucket,
+      const base_manifest& manifest,
+      const remote_manifest_path& key,
+      retry_chain_node& parent);
+
     /// \brief Upload segment to S3
     ///
     /// The method uploads the segment while tolerating some errors. It can