Allow ** glob pattern in sync parameters

[pehlert]

This change allows to use the doublestar (**) pattern in the sync parameters for recursive sync of deep folder structures.

It will hopefully not break compatibility with existing use cases, but as I only started working with skaffold, I cannot guarantee this. Test cases are still passing at least.

If desired, I can also add a new example illustrating the use of this.

Syntax example:

sync:
    app/src/**/*.js: app/src
    app/css/**/*.css: app/css
    html/*.html: static/

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[balopat]

@pehlert can you please rebase and sign the CLA? This looks good, I'm open to merge it.

[googlebot]

CLAs look good, thanks!

[codecov-io]

Codecov Report

Merging #1266 into master will increase coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1266      +/-   ##
==========================================
+ Coverage   44.24%   44.26%   +0.02%     
==========================================
  Files         104      104              
  Lines        4629     4631       +2     
==========================================
+ Hits         2048     2050       +2     
  Misses       2372     2372              
  Partials      209      209

Impacted Files	Coverage Δ
pkg/skaffold/sync/sync.go	91.17% <100%> (+0.26%)	⬆️

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[pehlert]

@balopat Took some back and forth as I didn't have a Windows box available for testing, but should be okay now.

[radityasurya]

would be nice if this could be merged for the next release 👍

[priyawadhwa]

@radityasurya thanks for your contribution!