enhance: doc gen: display attributes in table

[amyXia1994]

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

• N
• Y

close #166

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

enhance: doc gen: display attributes in table

the file generated can be seen here:
https://github.com/amyXia1994/kcl-go/blob/enhance/doc-gen-attr-table/pkg/tools/gen/testdata/doc/pkg/md/main.md

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

[coveralls]

Pull Request Test Coverage Report for Build 6664464256

• 10 of 11 (90.91%) changed or added relevant lines in 2 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.02%) to 65.616%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pkg/tools/gen/genopenapi.go	8	9	88.89%

Files with Coverage Reduction	New Missed Lines	%
pkg/tools/gen/genopenapi.go	1	89.2%

Totals
Change from base Build 6664117545:	-0.02%
Covered Lines:	2622
Relevant Lines:	3996

---

💛 - Coveralls

[Peefy]

LGTM