Add support for PDB and TopologySpreadConstraints

[micrOsman]

• Breaking change? (if so, please describe the impact and migration path for existing application instances)

What changes did you make? (Give an overview)

This PR is created to add support for Pod Disruption Budget, Pod Topology Spread Constraints and Pod Priority Class. The reason is to enhance the availability, reliability, and resiliency of the Kafka-UI, especially during updates and unexpected situations.
Fixes #3

Is there anything you'd like reviewers to focus on?

How Has This Been Tested? (put an "x" (case-sensitive!) next to an item)

• No need to
• Manually (please, describe, if necessary)
• Unit checks
• Integration checks
• Covered by existing automation

It was tested locally using a local cluster and another remote cluster.

Values added to value.yaml file used for my local tests were the following:

## Set Pod Priority Class - importance of Pod relatives to other pods.
##
priorityClassName: default

## Application controller Pod Disruption Budget
## Ref: https://kubernetes.io/docs/tasks/run-application/configure-pdb/
podDisruptionBudget:
  enabled: true
  minAvailable: "50%"
  maxUnavailable: ""

topologySpreadConstraints:
  - maxSkew: 1
    topologyKey: kubernetes.io/hostname
    whenUnsatisfiable: DoNotSchedule

This is the command used to execute the Helm Chart:
helm install kafka-ui -f .\kafka-ui\values.yaml .\kafka-ui\ -n kafka

Checklist (put an "x" (case-sensitive!) next to all the items, otherwise the build will fail)

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (e.g. ENVIRONMENT VARIABLES)
• My changes generate no new warnings (e.g. Sonar is happy)
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged

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[Narekmat]

Hello @micrOsman
Please change version in Chart.yaml file to 0.7.3

[micrOsman]

Hello @micrOsman Please change version in Chart.yaml file to 0.7.3

Hello @Narekmat, thank you for the review. The version has been increased to 0.7.3 and the app version increased to the current one.

[micrOsman]

Hello, Is there anything I can do to help implement these changes?

[Haarolean]

@micrOsman hey, sorry, figured out I haven't subscribed to this particular repo for some reason. We'll take a look

[Narekmat]

@micrOsman please check this.
Seems some issue with k8s 1.18.0 version.
https://github.com/provectus/kafka-ui-charts/pull/9/checks

[micrOsman]

Narekmat could you please run one more build-and-test job?