feat: doc gen: support generate package doc in a single page; add ref link

[amyXia1994]

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

• N
• Y
  [Enhancement]support an option to display schema attributes in a flatten way #164

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

pkg/tools/gen/gendoc.go
pkg/tools/gen/genopenapi.go

templates:
pkg/tools/gen/templates/doc/packageDoc.gotmpl
pkg/tools/gen/templates/doc/schemaDoc.gotmpl
pkg/tools/gen/templates/doc/schemaListDoc.gotmpl

tests:
pkg/tools/gen/gendoc_test.go
pkg/tools/gen/testdata/doc/...

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

feat: doc gen:

• support generate package doc in a single page;
• add ref link between schemas

• 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

[Peefy]

LGTM

[coveralls]

Pull Request Test Coverage Report for Build 6663959659

• 30 of 43 (69.77%) changed or added relevant lines in 2 files are covered.
• 3 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.3%) to 65.631%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pkg/tools/gen/genopenapi.go	14	16	87.5%
pkg/tools/gen/gendoc.go	16	27	59.26%

Files with Coverage Reduction	New Missed Lines	%
pkg/tools/gen/genopenapi.go	3	89.84%

Totals
Change from base Build 6662552616:	-0.3%
Covered Lines:	2620
Relevant Lines:	3992

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💛 - Coveralls