Consolidate processor configurations for actions when there're key conflicts

[oeyh]

Is your feature request related to a problem? Please describe.
These processors have similar overwrite_if_key_exists options:

• add_entries
• copy_values
• rename_keys
• parse_json
• parse_ion
• key_value

grok processor has a keys_to_overwrite option so that you can determine to overwrite or append (default) for each grok generated field.

There are 3 basic options when adding fields but the key already exists: overwrite, append or skip. We should consider making the options available and consistent throughout processors.

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Additional context
See comments from #4143