check secret target is an absolute windows path

[ndeloof]

What I did
As we check secret target is absolute, we need to consider both unix and windows absolute path syntaxes
we could be more deterministic relying on image platform to only run the relevant code, but doesn't seem there are major risks for confusion

Related issue
fixes #10817

(not mandatory) A picture of a cute animal, if possible in relation to what you did

[codecov]

Codecov Report

Patch coverage: 67.50% and project coverage change: +0.12 🎉

Comparison is base (5a072b1) 59.42% compared to head (47778f8) 59.55%.

Additional details and impacted files

@@            Coverage Diff             @@
##               v2   #10819      +/-   ##
==========================================
+ Coverage   59.42%   59.55%   +0.12%     
==========================================
  Files         115      115              
  Lines        9896     9909      +13     
==========================================
+ Hits         5881     5901      +20     
+ Misses       3426     3414      -12     
- Partials      589      594       +5     

Impacted Files	Coverage Δ
cmd/compose/config.go	33.54% <0.00%> (+0.61%)	⬆️
pkg/api/api.go	42.30% <ø> (-1.09%)	⬇️
pkg/compose/secrets.go	63.07% <0.00%> (ø)
pkg/compose/pull.go	75.62% <33.33%> (-1.11%)	⬇️
pkg/compose/create.go	58.99% <41.66%> (-0.50%)	⬇️
pkg/compose/build.go	74.43% <100.00%> (+0.89%)	⬆️
pkg/compose/build_classic.go	52.56% <100.00%> (+0.30%)	⬆️
pkg/compose/viz.go	100.00% <100.00%> (ø)

... and 2 files with indirect coverage changes

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[milas]

We do have a version of this that looks like it might be slightly more robust in compose-go already: https://github.com/compose-spec/compose-go/blob/95ac1be8bfdc4dc21cdfb14e37b52c31275046a3/loader/windows_path.go#L32-L43

(and it has test coverage 😉)

I think we should export & clean up the naming (s/isAbs/IsWindowsAbs/) from compose-go and switch to them here, but this should unblock all but the most pathological cases so LGTM 👍🏻