Do not update unmodifiable fields for StatefulSet

[jiangpengcheng]

(If this PR fixes a github issue, please add Fixes #<xyz>.)

Fixes #638

(or if this PR is one task of a github issue, please add Master Issue: #<xyz> to link to the master issue.)

Master Issue: #

Motivation

StatefulSet.spec only allow to update below fields:

• replicas
• template
• updateStrategy
• persistentVolumeClaimRetentionPolicy
• minReadySeconds

while during version upgrade of FM, Selector field is changed even with same yaml, and other fields maybe changed in further development too, such as:

• PodManagementPolicy
• ServiceName
• VolumeClaimTemplates

we need to ensure these changed won't update old existing statefulset

Modifications

Do not update unmodifiable fields for StatefulSet

Verifying this change

• Make sure that the change passes the CI checks.

(Please pick either of the following options)

This change is a trivial rework / code cleanup without any test coverage.

(or)

This change is already covered by existing tests, such as (please describe tests).

(or)

This change added tests and can be verified as follows:

(example:)

• Added integration tests for end-to-end deployment with large payloads (10MB)
• Extended integration test for recovery after broker failure

Documentation

Check the box below.

Need to update docs?

• doc-required

  (If you need help on updating docs, create a doc issue)

• no-need-doc

  (Please explain why)

• doc

  (If this PR contains doc changes)