feat: add go plugin APIs and examples

[Peefy]

1. Does this PR affect any open issues?(Y/N) and add issue references (e.g. "fix #123", "re #123".):

• N
• Y

feat: add go plugin APIs and examples

2. What is the scope of this PR (e.g. component or file name):

• pkg/native/**

3. Provide a description of the PR(e.g. more details, effects, motivations or doc link):

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Other

4. Are there any breaking changes?(Y/N) and describe the breaking changes(e.g. more details, motivations or doc link):

• N
• Y

5. Are there test cases for these changes?(Y/N) select and add more details, references or doc links:

• Unit test
• Integration test
• Benchmark (add benchmark stats below)
• Manual test (add detailed scripts or steps below)
• Other

• examples/plugin/main.go
• pkg/native/api_test.go
• pkg/native/client_test.go

[zong-zhe]

LGTM

[coveralls]

Pull Request Test Coverage Report for Build 8001919370

Details

• -50 of 173 (71.1%) changed or added relevant lines in 11 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.3%) to 63.261%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
kclvm.go	0	2	0.0%
pkg/kcl/api.go	14	16	87.5%
pkg/plugin/plugin.go	0	4	0.0%
pkg/native/api.go	14	19	73.68%
pkg/native/loader.go	16	22	72.73%
pkg/native/cgo.go	21	32	65.63%
pkg/native/client.go	43	63	68.25%

Files with Coverage Reduction	New Missed Lines	%
pkg/kcl/api.go	1	48.4%

Totals
Change from base Build 8000238102:	0.3%
Covered Lines:	3127
Relevant Lines:	4943

---

💛 - Coveralls