✨ add trace spans and metrics for agent-ngt and index-manager

[rinx]

Description:

• add trace spans for several functions that called by daemons
• add metrics about create index execution (agent)
• add initial_delay_max_duration that affects to start auto-index daemon after random duration within it.

Related Issue:

#343

How Has This Been Tested?:

nothing.

Environment:

• Golang Version: 1.14.3
• Docker Version: 19.03.8
• Kubernetes Version: 1.18.2
• NGT Version: 1.11.5

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.

[pull-assistant]

Best reviewed: commit by commit

---

Optimal code review plan

     📈 Add trace spans to agent-ngt and manager-in...

     📈 Add completed_create_index_total metric

     ✅ Fix tests

     ✨ Add initial_delay_max_duration to ngt

     ♻️ Revise calculation of initial duration

     Update pkg/agent/ngt/service/ngt.go

     🤖 Update license headers and formatting go codes

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[codecov]

Codecov Report

Merging #389 into master will decrease coverage by 0.02%.
The diff coverage is 0.00%.

@@            Coverage Diff            @@
##           master    #389      +/-   ##
=========================================
- Coverage    7.91%   7.88%   -0.03%     
=========================================
  Files         356     356              
  Lines       18319   18380      +61     
=========================================
  Hits         1450    1450              
- Misses      16660   16721      +61     
  Partials      209     209              

Impacted Files	Coverage Δ
internal/config/ngt.go	0.00% <0.00%> (ø)
internal/observability/metrics/agent/ngt/ngt.go	0.00% <0.00%> (ø)
pkg/agent/ngt/handler/grpc/handler.go	0.00% <0.00%> (ø)
pkg/agent/ngt/service/ngt.go	0.00% <0.00%> (ø)
pkg/manager/index/service/indexer.go	0.00% <0.00%> (ø)

---

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[rinx]

/rebase

[vdaas-ci]

[WARNING] Changes in interal/config may require you to change Helm charts. Please check.

[kpango]

/format
/approve

[vdaas-ci]

[WARNING] Changes in interal/config may require you to change Helm charts. Please check.

[vdaas-ci]

[FORMAT] Updating license headers and formatting go codes triggered by kpango.

[vdaas-ci]

[APPROVED] This PR is approved by kpango.

[vdaas-ci]

[WARNING] Changes in interal/config may require you to change Helm charts. Please check.