feat: add workspace domain model

[healthjyk]

What type of PR is this?

/kind feature

What this PR does / why we need it:

add domain model of workspace management.

Which issue(s) this PR fixes:

Fixes #617

Special notes for your reviewer:

For the backend config, should be completed later.

[healthjyk]

This is an upgrade of #618

[coveralls]

Pull Request Test Coverage Report for Build 7044411843

Warning: This coverage report may be inaccurate.

We've detected an issue with your CI configuration that might affect the accuracy of this pull request's coverage report.
To ensure accuracy in future PRs, please see these guidelines.
A quick fix for this PR: rebase it; your next report should be accurate.

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 19 unchanged lines in 3 files lost coverage.
• Overall coverage decreased (-0.1%) to 74.948%

---

Files with Coverage Reduction	New Missed Lines	%
pkg/engine/operation/parser/spec_parser.go	4	56.1%
pkg/engine/operation/parser/parser.go	6	75.61%
pkg/modules/util.go	9	70.29%

Totals
Change from base Build 7028690290:	-0.1%
Covered Lines:	6486
Relevant Lines:	8654

---

💛 - Coveralls

[SparkYuan]

lgtm