feat: support unmarshal KCL union to AppConfiguration

[panshuai-ps]

What type of PR is this?

/kind feature

What this PR does / why we need it:

Support unmarshal KCL union to AppConfiguration

Which issue(s) this PR fixes:

Fixes #

[coveralls]

Pull Request Test Coverage Report for Build 5898591895

• 4 of 7 (57.14%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.04%) to 71.916%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pkg/generator/appconfiguration/generator/app_configurations_generator.go	0	1	0.0%
pkg/generator/kcl/kcl_generator.go	4	6	66.67%

Totals
Change from base Build 5888275489:	0.04%
Covered Lines:	5211
Relevant Lines:	7246

---

💛 - Coveralls

[SparkYuan]

lgtm