move template out from extension to spec.template

[wonderflow]

fix #976

I still keep the compatibility for extension.template, so the existing definition file won't fail.

[codecov]

Codecov Report

Merging #1014 (34ae24c) into master (b6f10bb) will decrease coverage by 0.03%.
The diff coverage is 26.98%.

@@            Coverage Diff             @@
##           master    #1014      +/-   ##
==========================================
- Coverage   38.33%   38.30%   -0.04%     
==========================================
  Files         114      114              
  Lines        9556     9574      +18     
==========================================
+ Hits         3663     3667       +4     
- Misses       5422     5430       +8     
- Partials      471      477       +6     

Flag	Coverage Δ
unittests	38.30% <26.98%> (-0.04%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pkg/appfile/parser.go	68.27% <0.00%> (ø)
pkg/commands/refresh.go	15.23% <ø> (ø)
...tiondeployment/applicationdeployment_controller.go	0.00% <0.00%> (ø)
pkg/plugins/capcenter.go	20.33% <0.00%> (ø)
pkg/oam/util/template.go	37.50% <31.81%> (+14.09%)	⬆️
pkg/plugins/cluster.go	47.26% <46.15%> (-1.72%)	⬇️
...dev/v1alpha2/traitdefinition/validating_handler.go	54.05% <66.66%> (-3.45%)	⬇️
cmd/core/main.go	20.25% <100.00%> (+0.50%)	⬆️
pkg/utils/apply/apply.go	95.74% <100.00%> (ø)
...andard.oam.dev/v1alpha1/routes/route_controller.go	65.47% <0.00%> (-4.17%)	⬇️
... and 2 more

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[zzxwill]

LGTM