Refactor constructing containers and support checkout certain git refs

[chivalryq]

In this PR, I

1. refactor the meta container building process. Use assembler to take the responsiblity for that.
2. support checking out certain git branch/tag/commit in Configuration. For example:

apiVersion: terraform.core.oam.dev/v1beta2
kind: Configuration
metadata:
  name: alibaba-oss-bucket-hcl-restore-example
spec:
  remote: https://github.com/user/repo
  gitRef:
    branch: feature
    # tag: v1.0.0
    # commit: 0f1875a6b760fe3c4dafc21415c554001e37bacd

If more than one entries is provided in gitRef. The priority order is:

commit > tag > branch

Fixes: #378

Signed-off-by: Qiaozp qiaozhongpei.qzp@alibaba-inc.com

[codecov]

Codecov Report

Patch coverage: 53.61% and project coverage change: -14.19% ⚠️

Comparison is base (3a96f68) 79.31% compared to head (6b95d00) 65.12%.
Report is 20 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #382       +/-   ##
===========================================
- Coverage   79.31%   65.12%   -14.19%     
===========================================
  Files          23       31        +8     
  Lines        1750     2145      +395     
===========================================
+ Hits         1388     1397        +9     
- Misses        278      659      +381     
- Partials       84       89        +5     

Flag	Coverage Δ
e2e	0.00% <0.00%> (∅)
unit	67.35% <53.66%> (-11.96%)	⬇️

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

Files Changed	Coverage Δ
controllers/configuration/configuration.go	92.22% <0.00%> (-3.19%)	⬇️
controllers/process/container/apply.go	0.00% <0.00%> (ø)
controllers/process/container/assembler.go	0.00% <0.00%> (ø)
controllers/process/container/init.go	0.00% <0.00%> (ø)
controllers/process/container/input.go	0.00% <0.00%> (ø)
controllers/provider/credentials.go	92.63% <ø> (ø)
e2e/normal/regression.go	0.00% <0.00%> (ø)
controllers/process/container/git.go	10.93% <10.93%> (ø)
controllers/configuration_controller.go	66.91% <49.25%> (-10.45%)	⬇️
controllers/terraform/logging.go	64.91% <50.00%> (ø)
... and 4 more

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