Add alpine to CI for source-build

Author: omajid

src/SourceBuild/Arcade/eng/common/templates/job/source-build-run-tarball-build.yml

@@ -12,6 +12,7 @@ parameters:
 
   # The following parameters aren't expected to be passed in rather they are used for encapsulation
   # -----------------------------------------------------------------------------------------------
+  alpine315Container: mcr.microsoft.com/dotnet-buildtools/prereqs:alpine-3.15-20211214164127-f0ea7ba
   centOS7Container: mcr.microsoft.com/dotnet-buildtools/prereqs:centos-7-source-build-20210714125450-5d87b80
   centOS8Container: mcr.microsoft.com/dotnet-buildtools/prereqs:centos-8-source-build-20211118190102-9355e7b
   debian9Container: mcr.microsoft.com/dotnet-buildtools/prereqs:debian-stretch-20211001171226-047508b
@@ -37,6 +38,12 @@ jobs:
       ${{ parameters.poolInternal }}
   strategy:
     matrix:
+      Alpine315-Offline:
+        _BootstrapPrep: true
+        _BuildArch: x64
+        _Container: ${{ parameters.alpine315Container }}
+        _ExcludeOmniSharpTests: true
+        _RunOnline: false
       CentOS7-Online:
         _BootstrapPrep: true
         _BuildArch: x64