Add changelog for v2.0.0-rc.0

[ChenYi015]

Purpose of this PR

Proposed changes:

• Add changelog for v2.0.0-rc.0
• Add changelog for spark-operator-chart-1.4.6
• Update VERSION file to v2.0.0-rc.0

Change Category

Indicate the type of change by marking the applicable boxes:

• Bugfix (non-breaking change which fixes an issue)
• Feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that could affect existing functionality)
• Documentation update

Rationale

Checklist

Before submitting your PR, please review the following:

• I have conducted a self-review of my own code.
• I have updated documentation accordingly.
• I have added tests that prove my changes are effective or that my feature works.
• Existing unit tests pass locally with my changes.

Additional Notes

[ChenYi015]

/assign @andreyvelich @vara-bonthu

[vara-bonthu]

/lgtm

[google-oss-prow]

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