GH2833: Add implicit bootstrapping of modules

[patriksvensson]

Closes #2833

[devlead]

dotnet-cake.exe ./build.cake --bootstrap should not execute script.

[patriksvensson]

@cake-build/cake-team Ready for review

[devlead]

I've taken this for a spin, afaik as I can see it works as intended i.e.

Test-Path .\tools\modules
.\tools\dotnet-cake.exe --target=Clean
Test-Path .\tools\modules

outputs

False
Tool GitVersion.Tool is already installed, with required version.
Tool SignClient is already installed, with required version.
Tool GitReleaseManager.Tool is already installed, with required version.

----------------------------------------
Setup
----------------------------------------
Calculating Semantic Version
Calculated Semantic Version: 1.0.0-GH-2833-0001
Building version 1.0.0-GH-2833-0001 of Cake (Release, Clean) using version 1.0.0.0 of Cake. (IsTagged: False)

========================================
Clean
========================================

----------------------------------------
Teardown
----------------------------------------
Starting Teardown...
Finished running tasks.

Task                          Duration
--------------------------------------------------
Setup                         00:00:01.0869588
Clean                         00:00:00.1628303
Teardown                      00:00:00.0054472
--------------------------------------------------
Total:                        00:00:01.2552363
True

First False in output = no module folder
Last True in output + that it starts = modules fetched and script executed

And running

Test-Path .\tools\modules
.\tools\dotnet-cake.exe build.cake --bootstrap
Test-Path .\tools\modules

outputs

False
True

First False in output = no module folder
Last True in output + nothing else= modules fetched but script not executed

[devlead]

@patriksvensson your changes have been merged, thanks for your contribution 👍