Conditionally disable `probe_platform_engines!` and `probe_symlink_creation`

[peteristhegreat]

The functions to disable or bypass are found here:

BinaryProvider.jl/src/PlatformEngines.jl

Line 168 in d57da3f

function probe_platform_engines!(;verbose::Bool = false)

and

BinaryProvider.jl/src/PlatformEngines.jl

Line 111 in d57da3f

function probe_symlink_creation(dest::AbstractString)

Both are noisy when using a precompiled binary version of Julia, a la PackageCompiler. There should be an environment variable or some other flag that could go in the precompile file or a top level global that can suppress these checks for setups where the correct package has already been downloaded and hooked in with BinaryProvider.

On a slim and secure docker container that doesn't have any downloader executables on it intentionally, BinaryProvider crashes when it can't find a binary for wget or curl or similar. Again the use case is a stripped, lightweight julia project that has just enough to run, but no longer needs to download or make new files.

And when deploying to Windows and running as non-admin, the symlink warning should have an override to not be visible, especially if in use with something like PackageCompiler.

Thank you for the excellent package. And keep up the great work.