Improve security manager

[hzxuzhonghu]

What type of PR is this?

/kind enhancement

What this PR does / why we need it:

It does many enhancements:

1. added a flag enable-secret-manager to allow turn off secret manager
2. Add a separate retry fetching cert
3. Removed reconnect, actually grpc connection can be reconnected automatically when the underlying connection closed.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 46 lines in your changes missing coverage. Please review.

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Flag	Coverage Δ
unittests	31.76% <0.00%> (?)

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Files	Coverage Δ
pkg/controller/security/option.go	0.00% <ø> (ø)
pkg/controller/security/caclient.go	0.00% <0.00%> (ø)
pkg/controller/controller.go	0.00% <0.00%> (ø)
pkg/controller/workload/workload_processor.go	13.46% <0.00%> (ø)
pkg/controller/security/manager.go	0.00% <0.00%> (ø)

[hzxuzhonghu]

Fix #405

[nlgwcy]

/lgtm
/approve

[kmesh-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: nlgwcy

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