Add support for custom metrics for HPA

[sanketsudake]

Description

Previous PR: #2421

Add new fields in Function Specification to autoscale function based on different metrics combination.

// hpaMetrics is the list of metrics used to determine the desired replica count of the Deployment
// created for the function.
// Applicable for executor type newdeploy and container.
// +optional
Metrics []asv2beta2.MetricSpec `json:"hpaMetrics,omitempty"`

// hpaBehavior is the behavior of HPA when scaling in up/down direction.
// Applicable for executor type newdeploy and container.
// +optional
Behavior *asv2beta2.HorizontalPodAutoscalerBehavior `json:"hpaBehavior,omitempty"`

Which issue(s) this PR fixes:

Fixes #854

Testing

Checklist:

• I ran tests as well as code linting locally to verify my changes.
• I have done manual verification of my changes, changes working as expected.
• I have added new tests to cover my changes.
• My changes follow contributing guidelines of Fission.
• I have signed all of my commits.

[codecov]

Codecov Report

Merging #2423 (bdfa9c2) into master (ed4bd25) will decrease coverage by 0.00%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##           master    #2423      +/-   ##
==========================================
- Coverage   17.42%   17.41%   -0.01%     
==========================================
  Files          60       60              
  Lines        6544     6539       -5     
==========================================
- Hits         1140     1139       -1     
+ Misses       5320     5317       -3     
+ Partials       84       83       -1     

Flag	Coverage Δ
unittests	17.41% <50.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pkg/fission-cli/cmd/function/list.go	0.00% <0.00%> (ø)
pkg/fission-cli/cmd/function/create.go	25.64% <57.14%> (+<0.01%)	⬆️

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