add support for multiple --tag flags in build (#785)

- Closes #732.

## Type of Change
- [ ] Bug fix
- [x] New feature  
- [ ] Breaking change
- [ ] Documentation update

## Motivation and Context
Adds support for specifying multiple `-t` / `--tag` flags with the
`build` command. All specified tags will point to the same built image.

Example:
`container build -t myapp:latest -t myapp:v1.0.0 -t myapp:stable .`

## Testing
- [x] Tested locally
- [x] Added/updated tests
- [x] Added/updated docs

Tests/CLITests/Subcommands/Build/CLIBuildBase.swift

@@ -83,7 +83,23 @@ class TestCLIBuildBase: CLITest {
         otherArgs: [String] = []
     ) throws -> String {
         try buildWithPaths(
-            tag: tag,
+            tags: [tag],
+            tempContext: tempDir,
+            tempDockerfileContext: tempDir,
+            buildArgs: buildArgs,
+            otherArgs: otherArgs
+        )
+    }
+
+    @discardableResult
+    func build(
+        tags: [String],
+        tempDir: URL,
+        buildArgs: [String] = [],
+        otherArgs: [String] = []
+    ) throws -> String {
+        try buildWithPaths(
+            tags: tags,
             tempContext: tempDir,
             tempDockerfileContext: tempDir,
             buildArgs: buildArgs,
@@ -95,7 +111,7 @@ class TestCLIBuildBase: CLITest {
     // the dockerfile path. If both paths are the same, use `build` func above.
     @discardableResult
     func buildWithPaths(
-        tag: String,
+        tags: [String],
         tempContext: URL,
         tempDockerfileContext: URL,
         buildArgs: [String] = [],
@@ -107,9 +123,11 @@ class TestCLIBuildBase: CLITest {
             "build",
             "-f",
             tempDockerfileContext.appendingPathComponent("Dockerfile").path,
-            "-t",
-            tag,
         ]
+        for tag in tags {
+            args.append("-t")
+            args.append(tag)
+        }
         for arg in buildArgs {
             args.append("--build-arg")
             args.append(arg)

Tests/CLITests/Subcommands/Build/CLIBuilderTest.swift

@@ -390,7 +390,7 @@ extension TestCLIBuildBase {
 
             let imageName = "registry.local/build-diff-context:\(UUID().uuidString)"
             #expect(throws: Never.self) {
-                try self.buildWithPaths(tag: imageName, tempContext: buildContextDir, tempDockerfileContext: dockerfileCtxDir)
+                try self.buildWithPaths(tags: [imageName], tempContext: buildContextDir, tempDockerfileContext: dockerfileCtxDir)
             }
             #expect(try self.inspectImage(imageName) == imageName, "expected to have successfully built \(imageName)")
         }
@@ -432,5 +432,29 @@ extension TestCLIBuildBase {
                 "expected platforms \(expected), got \(actual)"
             )
         }
+
+        @Test func testBuildMultipleTags() throws {
+            let tempDir: URL = try createTempDir()
+            let dockerfile: String =
+                """
+                FROM scratch
+
+                ADD emptyFile /
+                """
+            let context: [FileSystemEntry] = [.file("emptyFile", content: .zeroFilled(size: 1))]
+            try createContext(tempDir: tempDir, dockerfile: dockerfile, context: context)
+
+            let uuid = UUID().uuidString
+            let tag1 = "registry.local/multi-tag-test:\(uuid)"
+            let tag2 = "registry.local/multi-tag-test:latest"
+            let tag3 = "registry.local/multi-tag-test:v1.0.0"
+
+            try self.build(tags: [tag1, tag2, tag3], tempDir: tempDir)
+
+            // Verify all three tags exist and point to the same image
+            #expect(try self.inspectImage(tag1) == tag1, "expected to have successfully built \(tag1)")
+            #expect(try self.inspectImage(tag2) == tag2, "expected to have successfully built \(tag2)")
+            #expect(try self.inspectImage(tag3) == tag3, "expected to have successfully built \(tag3)")
+        }
     }
 }