Fix file lock issue with MSBuild's /bl flag and the metro bundler

[dannyvv]

Periodically there is a locking issue when building vnext/Microsoft.ReactNative.sln when building with flag /bl. This flag tells msbuild to construct a detailed binary log. As it is constructing the log it is creating a .zip file to contain all the build specs. In the solution the IntegrationTest project runs the metro bundler. This one tries to open the .zip file and gets a file access violationand fails the build.
This change adds it to the metro config's exclusion list so it won't try to read that zip file.

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[ghost]

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[kmelmon]

[asklar]

@dannyvv I thought I had fixed these with #5050 - did I miss this one?

[dannyvv]

@dannyvv Danny van Velzen FTE I thought I had fixed these with #5050 - did I miss this one?

@asklar You correctly did all the apps, but it turns out our main solution runs a 'test' app in the inetegration test (npx spawned from msbuild to construct the bundle through custom targets) that picks up the metro-config in /vnext. You'd only see it if you locally run msbuild in the vnext folder with /bl. The CI builds it from the root giving msbuild a relative path so the zip file is written to the root of the enlistmnet outside of the purvue of the bundler.