doc: update docs of kusion concepts

[liu-hm19]

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

• N
• Y

fix #525

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

docs/kusion/3-concepts/
docs_versioned_docs/version-v0.12/3-concepts/

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

This PR adds the documentations to explain the concept of Release.

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

6. Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

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Name	Status	Preview	Comments	Updated (UTC)
kusionstack	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Jul 29, 2024 6:48am

[SparkYuan]

lgtm