Use CONTENT_ANNOTATION in more places, change name

Use the `const` we defined so it's easy to find the uses of it.
Also, change the name to be "namespaced" more clearly;
see https://github.com/opencontainers/image-spec/blob/main/annotations.md
for more.

lib/src/chunking.rs

@@ -10,6 +10,7 @@ use std::num::NonZeroU32;
 use std::rc::Rc;
 use std::time::Instant;
 
+use crate::container::CONTENT_ANNOTATION;
 use crate::objectsource::{ContentID, ObjectMeta, ObjectMetaMap, ObjectSourceMeta};
 use crate::objgv::*;
 use crate::statistics;
@@ -32,7 +33,6 @@ pub(crate) type ChunkMapping = BTreeMap<RcStr, (u64, Vec<Utf8PathBuf>)>;
 
 const LOW_PARTITION: &str = "2ls";
 const HIGH_PARTITION: &str = "1hs";
-const CONTENT_ANNOTATION: &str = "Content";
 
 #[derive(Debug, Default)]
 pub(crate) struct Chunk {

lib/src/container/encapsulate.rs

@@ -1,7 +1,7 @@
 //! APIs for creating container images from OSTree commits
 
 use super::ocidir::{Layer, OciDir};
-use super::{ocidir, OstreeImageReference, Transport};
+use super::{ocidir, OstreeImageReference, Transport, CONTENT_ANNOTATION};
 use super::{ImageReference, SignatureSource, OSTREE_COMMIT_LABEL};
 use crate::chunking::{Chunk, Chunking, ObjectMetaSized};
 use crate::container::skopeo;
@@ -151,19 +151,17 @@ fn export_chunked(
         .clone();
 
     // Add the ostree layer
-    let mut annotation_ostree_layer = HashMap::new();
-    annotation_ostree_layer.insert("Content".to_string(), "ostree_commit".to_string());
     ociw.push_layer(
         manifest,
         imgcfg,
         ostree_layer,
         description,
-        Some(annotation_ostree_layer),
+        None,
     );
     // Add the component/content layers
     for (layer, name, packages) in layers {
         let mut annotation_component_layer = HashMap::new();
-        annotation_component_layer.insert("Content".to_string(), packages.join(","));
+        annotation_component_layer.insert(CONTENT_ANNOTATION.to_string(), packages.join(","));
         ociw.push_layer(
             manifest,
             imgcfg,

lib/src/container/mod.rs

@@ -37,6 +37,10 @@ use std::str::FromStr;
 /// The label injected into a container image that contains the ostree commit SHA-256.
 pub const OSTREE_COMMIT_LABEL: &str = "ostree.commit";
 
+/// The name of an annotation attached to a layer which names the packages/components
+/// which are part of it.
+pub(crate) const CONTENT_ANNOTATION: &str = "ostree.components";
+
 /// Our generic catchall fatal error, expected to be converted
 /// to a string to output to a terminal or logs.
 type Result<T> = anyhow::Result<T>;