Add default launchSettings.json

[filzrev]

Purpose of this PR
This PR add default launchSettings.json to docfx project.

These change can make the following work easier.

• Debugging docfx.exe project with default docs.
• Debug docfx.exe project with custom target. (It need to modify docfx.json path in config)

Defined Profiles
Following profiles are defined.

Profile Name	Description
docfx build	(Default)
docfx metadata
docfx serve	With --open-browser option
docfx

Usage
Launch profile's can be selected by Visual Studio navigation menu.

When docfx build profile selected. Ctrl+F5 starts docfx build command.
And docfx serve profile selected. Ctrl+F5 starts docfx serve --open-browser command.

Notes
launchSettings.json is excluded by project's .gitignore. and considered as per-user settings.
When this PR is merged. It may cause file conflicts if user already using custom launchSettings.json.
In that case. user needs to ignore updated content explicitly.

I thought this operation burden is acceptable.
Because project's default launchSettings.json is rarely changed from now on.
.

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: -0.01 ⚠️

Comparison is base (1263a81) 77.05% compared to head (7810a5e) 77.04%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8935      +/-   ##
==========================================
- Coverage   77.05%   77.04%   -0.01%     
==========================================
  Files         605      605              
  Lines       25042    25042              
==========================================
- Hits        19295    19294       -1     
- Misses       5747     5748       +1     

see 1 file with indirect coverage changes

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