Add backoff metrics panel

[hlts2]

Description:

WHAT

This PR contains the following changes

• add backoff metrics dashboard
• add Completed RPCs/Latency panel for LB, Agent
• fix query (irate->increase) for gc count panel

WHY

We added new feature to get backoff metrics. So we need to create new panel to grafana.
And OSS grafana's dashboard was old, so we need to change the latest.

Related Issue:

How Has This Been Tested?:

Environment:

• Go Version: 1.18.2
• Docker Version: 20.10.8
• Kubernetes Version: 1.22.0
• NGT Version: 1.14.5

Types of changes:

• Bug fix [type/bug]
• New feature [type/feature]
• Add tests [type/test]
• Security related changes [type/security]
• Add documents [type/documentation]
• Refactoring [type/refactoring]
• Update dependencies [type/dependency]
• Update benchmarks and performances [type/bench]
• Update CI [type/ci]

Changes to Core Features:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your core changes, as applicable?
• Have you successfully ran tests with your changes locally?

Checklist:

• I have read the CONTRIBUTING document.
• I have checked open Pull Requests for the similar feature or fixes?
• I have added tests and benchmarks to cover my changes.
• I have ensured all new and existing tests passed.
• I have commented my code, particularly in hard-to-understand areas
• I have updated the documentation accordingly.

[vdaas-ci]

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[hlts2]

📝 The following image is result for my local environment.

[kpango]

LGTM

[hlts2]

@kpango @datelier
Thank you for your review!
I will merge this PR!