Add an option to suppress the legal banner on each run

## Issue Description ##
## Steps to Reproduce ##
1. Open a C# project.
2. Run the project

## Expected Behavior ##
Seeing the uncluttered output of my code.

## Actual Behavior ##
```
-------------------------------------------------------------------
You may only use the Microsoft .NET Core Debugger (vsdbg) with
Visual Studio Code, Visual Studio or Visual Studio for Mac software
to help you develop and test your applications.
-------------------------------------------------------------------
```
```
my output
```

## Reason ##
The banner may provide useful information on the first 1-10 runs, but since then, at best it only consumes the precious space for your program output, at worst it reminds you that the first most important thing about whatever you are trying to achieve is the fact that MS employ a legal dept.

## Logs ##

### OmniSharp log ###
Post the output from Output-->OmniSharp log here

### C# log ###
Post the output from Output-->C# here

## Environment information ##

**VSCode version**: 1.43.2
**C# Extension**: 1.21.16

Dotnet Information
.NET Core SDK (reflecting any global.json):
Version: 3.1.201
Commit: b1768b4ae7

Runtime Environment:
OS Name: Windows
OS Version: 10.0.18363
OS Platform: Windows
RID: win10-x64
Base Path: C:\Program Files\dotnet\sdk\3.1.201\

Host (useful for support):
Version: 3.1.3
Commit: 4a9f85e9f8

.NET Core SDKs installed:
2.1.509 [C:\Program Files\dotnet\sdk]
3.1.101 [C:\Program Files\dotnet\sdk]
3.1.200 [C:\Program Files\dotnet\sdk]
3.1.201 [C:\Program Files\dotnet\sdk]

.NET Core runtimes installed:
Microsoft.AspNetCore.All 2.1.1 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.13 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.17 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.App 2.1.1 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.13 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.17 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.1 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.2 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.3 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.NETCore.App 2.1.13 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.17 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.1 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.2 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.3 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.WindowsDesktop.App 3.1.1 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 3.1.2 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 3.1.3 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

To install additional .NET Core runtimes or SDKs:
https://aka.ms/dotnet-download

Visual Studio Code Extensions

|Extension|Author|Version|
|---|---|---|
|csharp|ms-dotnettools|1.21.16|
|debugger-for-chrome|msjsdiag|4.12.6|
|dotnetscriptr|Wivuu|0.2.3|
|gc-excelviewer|GrapeCity|2.1.34|
|gitlens|eamodio|10.2.1|
|html-slim-scss-css-class-completion|gencer|1.5.23|
|lorem-ipsum|Tyriar|1.2.0|
|markdown-all-in-one|yzhang|2.7.0|
|markdown-pdf|yzane|1.4.4|
|monitor-file|rkostrzewski|1.0.1|
|mssql|ms-mssql|1.9.0|
|nunjucks-template|eseom|0.2.1|
|powershell|ms-vscode|2020.3.0|
|python|ms-python|2020.3.71659|
|quicktype|quicktype|12.0.46|
|remote-wsl|ms-vscode-remote|0.42.4|
|render-crlf|medo64|1.5.1|
|scss-refactoring|lukazakrajsek|0.1.4|
|sftp|liximomo|1.12.9|
|smarty|imperez|0.3.0|
|swig|zhutian|0.0.5|
|theme-sapphire|Tyriar|0.9.1|
|vs-code-xml-format|fabianlauer|0.1.5|
|vs-html-to-css|neptunedesign|1.0.0|
|vscode-auto-scroll|pejmannikram|1.0.3|
|vscode-autohotkey|slevesque|0.2.2|
|vscode-css-formatter|aeschli|1.0.1|
|vscode-docker|ms-azuretools|1.0.0|
|vscode-file-peek|abierbaum|1.0.1|
|vscode-great-icons|emmanuelbeziat|2.1.47|
|vscode-scss|mrmlnc|0.9.0|
|vscode-scss-formatter|sibiraj-s|2.0.0|
|vscodeintellicode|VisualStudioExptTeam|1.2.6|;