Add init methods for all the members of the Flags type (#1203)

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

## Motivation and Context
Authors of CLI plugins for container will be able to reuse the container
flags defined in the CLI package, instead of having to duplicate them in
their project

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

Author: adityaramani

Sources/Services/ContainerAPIService/Client/Flags.swift

@@ -22,13 +22,39 @@ public struct Flags {
     public struct Logging: ParsableArguments {
         public init() {}
 
+        public init(debug: Bool) {
+            self.debug = debug
+        }
+
         @Flag(name: .long, help: "Enable debug output [environment: CONTAINER_DEBUG]")
         public var debug = false
     }
 
     public struct Process: ParsableArguments {
         public init() {}
 
+        public init(
+            cwd: String?,
+            env: [String],
+            envFile: [String],
+            gid: UInt32?,
+            interactive: Bool,
+            tty: Bool,
+            uid: UInt32?,
+            ulimits: [String],
+            user: String?
+        ) {
+            self.cwd = cwd
+            self.env = env
+            self.envFile = envFile
+            self.gid = gid
+            self.interactive = interactive
+            self.tty = tty
+            self.uid = uid
+            self.ulimits = ulimits
+            self.user = user
+        }
+
         @Option(name: .shortAndLong, help: "Set environment variables (key=value, or just key to inherit from host)")
         public var env: [String] = []
 
@@ -75,6 +101,11 @@ public struct Flags {
     public struct Resource: ParsableArguments {
         public init() {}
 
+        public init(cpus: Int64?, memory: String?) {
+            self.cpus = cpus
+            self.memory = memory
+        }
+
         @Option(name: .shortAndLong, help: "Number of CPUs to allocate to the container")
         public var cpus: Int64?
 
@@ -88,6 +119,13 @@ public struct Flags {
     public struct DNS: ParsableArguments {
         public init() {}
 
+        public init(domain: String?, nameservers: [String], options: [String], searchDomains: [String]) {
+            self.domain = domain
+            self.nameservers = nameservers
+            self.options = options
+            self.searchDomains = searchDomains
+        }
+
         @Option(
             name: .customLong("dns"),
             help: .init("DNS nameserver IP address", valueName: "ip")
@@ -127,6 +165,58 @@ public struct Flags {
     public struct Management: ParsableArguments {
         public init() {}
 
+        public init(
+            arch: String,
+            cidfile: String,
+            detach: Bool,
+            dns: Flags.DNS,
+            dnsDisabled: Bool,
+            entrypoint: String?,
+            initImage: String?,
+            kernel: String?,
+            labels: [String],
+            mounts: [String],
+            name: String?,
+            networks: [String],
+            os: String,
+            platform: String?,
+            publishPorts: [String],
+            publishSockets: [String],
+            readOnly: Bool,
+            remove: Bool,
+            rosetta: Bool,
+            runtime: String?,
+            ssh: Bool,
+            tmpFs: [String],
+            virtualization: Bool,
+            volumes: [String]
+        ) {
+            self.arch = arch
+            self.cidfile = cidfile
+            self.detach = detach
+            self.dns = dns
+            self.dnsDisabled = dnsDisabled
+            self.entrypoint = entrypoint
+            self.initImage = initImage
+            self.kernel = kernel
+            self.labels = labels
+            self.mounts = mounts
+            self.name = name
+            self.networks = networks
+            self.os = os
+            self.platform = platform
+            self.publishPorts = publishPorts
+            self.publishSockets = publishSockets
+            self.readOnly = readOnly
+            self.remove = remove
+            self.rosetta = rosetta
+            self.runtime = runtime
+            self.ssh = ssh
+            self.tmpFs = tmpFs
+            self.virtualization = virtualization
+            self.volumes = volumes
+        }
+
         @Option(name: .shortAndLong, help: "Set arch if image can target multiple architectures")
         public var arch: String = Arch.hostArchitecture().rawValue
 
@@ -235,6 +325,10 @@ public struct Flags {
     public struct Progress: ParsableArguments {
         public init() {}
 
+        public init(progress: ProgressType) {
+            self.progress = progress
+        }
+
         public enum ProgressType: String, ExpressibleByArgument {
             case none
             case ansi
@@ -247,6 +341,10 @@ public struct Flags {
     public struct ImageFetch: ParsableArguments {
         public init() {}
 
+        public init(maxConcurrentDownloads: Int) {
+            self.maxConcurrentDownloads = maxConcurrentDownloads
+        }
+
         @Option(name: .long, help: "Maximum number of concurrent downloads (default: 3)")
         public var maxConcurrentDownloads: Int = 3
     }