feat: GitDownloader supports cache

[zong-zhe]

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

• N
• Y

re #384

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

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

[Peefy]

LGTM

[coveralls]

Pull Request Test Coverage Report for Build 11551360709

Details

• 57 of 109 (52.29%) changed or added relevant lines in 4 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.2%) to 41.72%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pkg/git/getter.go	7	9	77.78%
pkg/downloader/source.go	11	16	68.75%
pkg/git/git.go	0	7	0.0%
pkg/downloader/downloader.go	39	77	50.65%

Totals
Change from base Build 11477327992:	0.2%
Covered Lines:	3653
Relevant Lines:	8756

---

💛 - Coveralls