Update default values of distribution and infrastructure fields

[bgriddaluru]

Goals

1. If user doesn't specify overrides for distro and/or infra, values should be calculated from heuristics . These values shouldn't be fixed during the onboarding time.
2. User should be able to override to generic value of distro and infra.

Issues

1. User is unable to override the values to generic
2. If the user doesn't specify any override values for distro or infra, these are calculated from heuristics and stored in config map. Cluster metadata agent considers values from config map as override and ignores the values calculated from heuristics
3. For update command supports distribution parameter and updates in CC resource but doesn't update in config map for agents.
   So old value in config map is unchanged.

Fixes

1. Since heuristics calculation is in cluster metadata agent, remove the duplicate logic from az cli.
2. If the user didn't specify any overrides, set the values in config map to empty string so that cluster metadata can use the heuristics values.
3. For update command, support infrastructure parameter. If these values are set, update the values in config map.

[github-actions]

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