Better input parameters validation for High Availability mode

[pablocarle]

Customer content

Is your feature request related to a problem? Please describe.
In an HA configuration scenario, when the properties for HA are set in the Zowe.yaml (haInstances section in the bottom)
If the startup is made without providing the HAINST STC parameter, the instance will start but services will use the externalDomain as default hostname for the services. This results in Discovery Service seeing only one instance per service.

Describe the solution you'd like
Zowe startup could validate that haInstances is set in zowe.yaml and prevent startup without specifying the HAINST property.

Describe alternatives you've considered
The logic to determine whether HA is enabled in the Zowe installation or not could be updated to use either HAINST or the haInstances section in yaml.

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Engineering team info (eg https://github.com/zowe/explorer-jes/issues/4)

As a [type of user],
I want [some goal]
so that [some reason].

Details/notes
[Detail - implementation notes]

Acceptance Criteria

*Scenario 1: [Title]
Given [context]
And [some more context]...
When [event]
Then [outcome]
 And [another outcome]...

[1000TurquoisePogs]

Maybe this behavior should only trigger if haInstances.size > 1.

I worry about existing users getting disrupted if for some reason they had haInstances defined but weren't using it. It would be user error but should they get disrupted?

If we put this change into v3, no problem. if we fix it in v2, would a disrupted user consider it a breaking change if they had haInstance.size > 1 and weren't using HAINST for some silly reason?

[balhar-jakub]

I am fine with putting the change in V3