Add configuration validation

[hongyuan1306]

I am a new user to curator and with the latest version of curator (4.0.0) I started with the following action config:

actions:
  1:
    action: delete_indices
    fitlers:
    - filtertype: pattern
      kind: prefix
      value: logstash-
    - filtertype: age
      source: name
      timestring: '%Y.%m.%d'
      direction: older
      unit: days
      unit_count: 5

Instead of 'filters' i typed in 'fitlers', which is a fairly common error to make.

As a result, all my indices in elastics are removed. And it took me some time to figure out why this happened.

I would suggest that curator provide better protection against this sort of disaster. For example, when unrecognized options are encountered, an error shall be raised.

As in SQL, a statement like DELETE FROM table_name WHRER 1=1 shall not delete any thing.

[untergeek]

I think that's worth pursuing.

As a rule, I advise using the --dry-run flag liberally when testing new configurations. The --dry-run flag is there so you can catch even legitimate configuration errors. I highly recommend it.

[hongyuan1306]

It was my fault not having spent time to carefully read the output of dry run.

Actually I did use --dry-run. But as a new user of curator, the output seems somewhat cryptic to understand. By the way, it did not say there was any error with my configuration. So I just let it go.

However, with due respect, it did show which indices were to be removed.

[evanvolgas]

Xref my stupid typo here: #730

Arguably some acceptable keywords in the config might make sense....