Add Alpine 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-3.15-20220809205726-94fc78a
   centOSStream8Container: mcr.microsoft.com/dotnet-buildtools/prereqs:centos-stream8-20220809204800-17a4aab
   centOSStream9Container: mcr.microsoft.com/dotnet-buildtools/prereqs:centos-stream9-20220107135047-4cd394c
   debian11Arm64Container: mcr.microsoft.com/dotnet-buildtools/prereqs:debian-11-arm64v8-20220812185233-b286fae
@@ -42,6 +43,12 @@ jobs:
         _EnablePoison: false
         _ExcludeOmniSharpTests: true
         _RunOnline: true
+      Alpine315-Offline:
+        _BootstrapPrep: true
+        _Container: ${{ parameters.alpine315Container }}
+        _EnablePoison: false
+        _ExcludeOmniSharpTests: true
+        _RunOnline: false
       ${{ if ne(variables['Build.Reason'], 'PullRequest') }}:
         CentOSStream8-Offline:
           _BootstrapPrep: false