Improve error display when there are invalid command line parameters

[normj]

Issue #, if available:
#1001

Description of changes:
Improve the error output to avoid dumping a stacktrace if there is a user error of an invalid command line parameter.

Before

> dotnet run -- help
Using launch settings from C:\codebase\aws-dotnet-deploy\src\AWS.Deploy.CLI\Properties\launchSettings.json...
AWS .NET deployment tool for deploying .NET Core applications to AWS.
Project Home: https://github.com/aws/aws-dotnet-deploy

Unhandled exception.  This is a bug.  Please copy the stack trace below and file a bug at https://github.com/aws/aws-dotnet-deploy.
Unknown command 'help'.
   at Spectre.Console.Cli.CommandTreeParser.ParseString(CommandTreeParserContext context, CommandTreeTokenStream stream, CommandTree node) in /_/src/Spectre.Console.Cli/Internal/Parsing/CommandTreeParser.cs:line 209
   at Spectre.Console.Cli.CommandTreeParser.ParseCommandParameters(CommandTreeParserContext context, CommandInfo command, CommandTree parent, CommandTreeTokenStream stream) in /_/src/Spectre.Console.Cli/Internal/Parsing/CommandTreeParser.cs:line 157
   at Spectre.Console.Cli.CommandTreeParser.Parse(CommandTreeParserContext context, CommandTreeTokenizerResult tokenizerResult) in /_/src/Spectre.Console.Cli/Internal/Parsing/CommandTreeParser.cs:line 82
   at Spectre.Console.Cli.CommandExecutor.InternalParseCommandLineArguments(CommandModel model, CommandAppSettings settings, IReadOnlyList`1 args) in /_/src/Spectre.Console.Cli/Internal/CommandExecutor.cs:line 213
   at Spectre.Console.Cli.CommandExecutor.ParseCommandLineArguments(CommandModel model, CommandAppSettings settings, IReadOnlyList`1 args) in /_/src/Spectre.Console.Cli/Internal/CommandExecutor.cs:line 133
   at Spectre.Console.Cli.CommandExecutor.Execute(IConfiguration configuration, IEnumerable`1 args) in /_/src/Spectre.Console.Cli/Internal/CommandExecutor.cs:line 74
   at Spectre.Console.Cli.CommandApp.RunAsync(IEnumerable`1 args) in /_/src/Spectre.Console.Cli/CommandApp.cs:line 87

After

> dotnet run -- help
Using launch settings from C:\codebase\aws-dotnet-deploy\src\AWS.Deploy.CLI\Properties\launchSettings.json...
AWS .NET deployment tool for deploying .NET Core applications to AWS.
Project Home: https://github.com/aws/aws-dotnet-deploy

Unknown command 'help'.

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 35.04%. Comparing base (fb656d3) to head (7774dc0).
⚠️ Report is 8 commits behind head on dev.

Files with missing lines	Patch %	Lines
src/AWS.Deploy.CLI/App.cs	0.00%	5 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##              dev    #1004       +/-   ##
===========================================
- Coverage   62.11%   35.04%   -27.08%     
===========================================
  Files         294      294               
  Lines       10813    10818        +5     
  Branches     1615     1616        +1     
===========================================
- Hits         6717     3791     -2926     
- Misses       3494     6681     +3187     
+ Partials      602      346      -256     

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