Propagate install_if and provider_priority to APKINDEX (#28899)

Resolves https://github.com/go-gitea/gitea/issues/28704

Example of an entry in the generated `APKINDEX` file:

```
C:Q1xCO3H9LTTEbhKt9G1alSC87I56c=
P:hello
V:2.12-r1
A:x86_64
T:The GNU Hello program produces a familiar, friendly greeting
U:https://www.gnu.org/software/hello/
L:GPL-3.0-or-later
S:15403
I:36864
o:hello
m:
t:1705934118
D:so:libc.musl-x86_64.so.1
p:cmd:hello=2.12-r1
i:foobar=1.0 !baz
k:42
```

the `i:` and `k:` entries are new.

---------

Co-authored-by: KN4CK3R <admin@oldschoolhack.me>

modules/packages/alpine/metadata.go

@@ -65,6 +65,7 @@ type FileMetadata struct {
 	InstallIf        string   `json:"install_if,omitempty"`
 	Provides         []string `json:"provides,omitempty"`
 	Dependencies     []string `json:"dependencies,omitempty"`
+	ProviderPriority int64    `json:"provider_priority,omitempty"`
 }
 
 // ParsePackage parses the Alpine package file
@@ -188,6 +189,11 @@ func ParsePackageInfo(r io.Reader) (*Package, error) {
 			if value != "" {
 				p.FileMetadata.Dependencies = append(p.FileMetadata.Dependencies, value)
 			}
+		case "provider_priority":
+			n, err := strconv.ParseInt(value, 10, 64)
+			if err == nil {
+				p.FileMetadata.ProviderPriority = n
+			}
 		}
 	}
 	if err := scanner.Err(); err != nil {

services/packages/alpine/repository.go

@@ -230,6 +230,12 @@ func buildPackagesIndex(ctx context.Context, ownerID int64, repoVersion *package
 		if len(pd.FileMetadata.Provides) > 0 {
 			fmt.Fprintf(&buf, "p:%s\n", strings.Join(pd.FileMetadata.Provides, " "))
 		}
+		if pd.FileMetadata.InstallIf != "" {
+			fmt.Fprintf(&buf, "i:%s\n", pd.FileMetadata.InstallIf)
+		}
+		if pd.FileMetadata.ProviderPriority > 0 {
+			fmt.Fprintf(&buf, "k:%d\n", pd.FileMetadata.ProviderPriority)
+		}
 		fmt.Fprint(&buf, "\n")
 	}