[Docs] Add xUnit output format in the command helper

[fred-maussion]

Env

• elastic-package v0.115.0 version-hash undefined (build time: unknown)
• MacOS

Is your feature request related to a problem? Please describe.

When executing elastic-package test --help we have cobertura,generic and stdout, file outpout format available but not for --report-format and website documentation doesn't mention the supported output format neither.

Flags:
      --coverage-format string   set format for coverage reports: cobertura,generic (default "cobertura")
      --defer-cleanup duration   defer test cleanup for debugging purposes
  -h, --help                     help for test
  -p, --profile string           select a profile to use for the stack configuration. Can also be set with ELASTIC_PACKAGE_PROFILE
      --report-format string     format of test report (default "human")
      --report-output string     output type for test report, eg: stdout, file (default "stdout")
      --test-coverage            enable test coverage reports

Solution

Add in the command helper the support of xUnit, human as an output

[fred-maussion]

Closing as part of #3044