De-dot 'kibana.version' in /package JSON responses

[andrewkroh]

This changes the response JSON from

  "conditions": {
    "kibana.version": "^7.15.0"
  },

to

  "conditions": {
    "kibana": {
      "version": "^7.15.0"
    }
  },

Closes #730

[elasticmachine]

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• Start Time: 2021-09-29T21:16:50.305+0000

• Duration: 6 min 32 sec

• Commit: d2d233f

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[mtojek]

I'm not sure if it doesn't mean that we break the API or just ... unwrap keys :) @ruflin WDYT ?

[ruflin]

This might break Fleet. @joshdover @jen-huang Lets make sure the team reviews / tests this before it gets in.

[jen-huang]

I tested this locally and did not see any breaking changes in Fleet, in fact we already had the de-dotted version typed:
https://github.com/elastic/kibana/blob/3eb93a84f52e1c884de06ce089fcd6f1dbbf23fa/x-pack/plugins/fleet/common/types/models/package_spec.ts#L54

I also tested the search endpoint that Fleet uses to query for packages which are compatible, i.e. /search?experimental=true&kibana.version=7.14.1 and that worked as expected too.