feat: add mysql/oss/s3 as new backends

[healthjyk]

What type of PR is this?

/kind feature

What this PR does / why we need it:

add mysql/oss/s3 as new backends

Which issue(s) this PR fixes:

Fixes #647

[coveralls]

Pull Request Test Coverage Report for Build 7136729595

• 61 of 141 (43.26%) changed or added relevant lines in 2 files are covered.
• 4 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.5%) to 74.477%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pkg/workspace/validation.go	61	76	80.26%
pkg/workspace/util.go	0	65	0.0%

Files with Coverage Reduction	New Missed Lines	%
pkg/workspace/validation.go	1	83.72%
pkg/engine/operation/parser/parser.go	3	79.27%

Totals
Change from base Build 7128953341:	-0.5%
Covered Lines:	6872
Relevant Lines:	9227

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💛 - Coveralls

[SparkYuan]

lgtm