Per-domain directories: changes apply on the next request, and one broken directory doesn't block reloads (DIR-17, DIR-21)

A write to x:Directory or Authentication reloads the directories at once,
here and across the cluster. A directory that fails to open is logged as
a warning against its id and becomes unavailable; before, it was a build
error, and any build error stopped every later reload from applying.

per_domain_directory_tests covers acceptance tests 1, 3, 4, 6, 7, 9, 11,
15 and 19 over SQL directories on SQLite files: each domain against its
own directory and the default, no fallback to internal passwords, a
directory answering for another directory's domain, aliases and groups
dropped, recipients through the directory and a 4xx while it's down, app
passwords while it's down, password changes refused and then allowed
after a move to the internal directory, linked directories, tenant
foreign keys, and changes taking effect without a reload.

crates/directory/src/core/config.rs

@@ -33,7 +33,9 @@ impl Directories {
             let directory = match result {
                 Ok(directory) => directory,
                 Err(err) => {
-                    bp.build_error(id, err.clone());
+                    // inbuxa: DIR-21: logged against the directory, which becomes
+                    // unavailable; the rest of the reload carries on
+                    bp.build_warning(id, err.clone());
                     Directory::Unavailable(UnavailableDirectory::new(directory_type, err))
                 }
             };
@@ -45,7 +47,7 @@ impl Directories {
             match directories.get(&(directory_id.id() as u32)) {
                 Some(default_directory) => default_directory.clone().into(),
                 None => {
-                    bp.build_error(
+                    bp.build_warning(
                         ObjectType::Authentication.singleton(),
                         format!("Default directory with ID {} not found", directory_id),
                     );