Prefer UTF-8 without BOM when writing Yaml

Fixes: #402

This is more commandline/unix friendly. Yaml allows a BOM but doesn't
require it, yaml documents without a BOM are specified to be utf-8.

src/Microsoft.Tye.Core/DeployApplicationKubernetesManifestStep.cs

@@ -32,7 +32,7 @@ namespace Microsoft.Tye
 
             {
                 await using var stream = File.OpenWrite(tempFile.FilePath);
-                await using var writer = new StreamWriter(stream, Encoding.UTF8, leaveOpen: true);
+                await using var writer = new StreamWriter(stream, new UTF8Encoding(encoderShouldEmitUTF8Identifier: false), leaveOpen: true);
 
                 await ApplicationYamlWriter.WriteAsync(output, writer, application);
             }

src/Microsoft.Tye.Core/DockerfileGenerator.cs

@@ -40,7 +40,7 @@ namespace Microsoft.Tye
             }
 
             await using var stream = File.OpenWrite(filePath);
-            await using var writer = new StreamWriter(stream, encoding: Encoding.UTF8, bufferSize: -1, leaveOpen: true);
+            await using var writer = new StreamWriter(stream, encoding: new UTF8Encoding(encoderShouldEmitUTF8Identifier: false), bufferSize: -1, leaveOpen: true);
 
             var entryPoint = project.AssemblyName;
             output.WriteDebugLine($"Writing Dockerfile to '{filePath}'.");

src/Microsoft.Tye.Core/GenerateApplicationKubernetesManifestStep.cs

@@ -22,7 +22,7 @@ namespace Microsoft.Tye
                 File.Delete(outputFilePath);
 
                 await using var stream = File.OpenWrite(outputFilePath);
-                await using var writer = new StreamWriter(stream, Encoding.UTF8, leaveOpen: true);
+                await using var writer = new StreamWriter(stream, new UTF8Encoding(encoderShouldEmitUTF8Identifier: false), leaveOpen: true);
 
                 await ApplicationYamlWriter.WriteAsync(output, writer, application);
             }

src/Microsoft.Tye.Core/ValidateSecretStep.cs

@@ -194,7 +194,7 @@ namespace Microsoft.Tye
 
             {
                 await using var stream = File.OpenWrite(tempFile.FilePath);
-                await using var writer = new StreamWriter(stream, Encoding.UTF8, bufferSize: -1, leaveOpen: true);
+                await using var writer = new StreamWriter(stream, new UTF8Encoding(encoderShouldEmitUTF8Identifier: false), bufferSize: -1, leaveOpen: true);
                 var yamlStream = new YamlStream(yaml.Select(y => y.Yaml));
                 yamlStream.Save(writer, assignAnchors: false);
             }

src/Microsoft.Tye.Core/WriteServiceYamlStep.cs

@@ -37,7 +37,7 @@ namespace Microsoft.Tye
             File.Delete(outputFilePath);
 
             using var stream = File.OpenWrite(outputFilePath);
-            using var writer = new StreamWriter(stream, Encoding.UTF8, bufferSize: -1, leaveOpen: true);
+            using var writer = new StreamWriter(stream, new UTF8Encoding(encoderShouldEmitUTF8Identifier: false), bufferSize: -1, leaveOpen: true);
             var yamlStream = new YamlStream(yaml.Select(y => y.Yaml));
             yamlStream.Save(writer, assignAnchors: false);