[Fix #812] Add the `ignore_unavailable` option to the request

[kolauren]

Add the ignore_unavailable option to the request: https://www.elastic.co/guide/en/elasticsearch/client/curator/current/option_ignore.html

This solves #812

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• [x] The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• [x] Wrote good commit messages.
• [x] Commit message starts with [Fix #issue-number] (if the related issue exists).
• [x] Feature branch is up-to-date with master (if not - rebase it).
• [x] Squashed related commits together.
• [x] Added tests.
• [x] Added an entry to the changelog if the new code introduces user-observable changes. See changelog entry format for details.

[rabotyaga]

Hey @kolauren 👋 ! Thanks for the contribution! Could you please change all links from curator reference to Elastcisearch reference: https://www.elastic.co/guide/en/elasticsearch/reference/current/multi-index.html#multi-index ?

[kolauren]

Updated the links!

[rabotyaga]

@kolauren Thank you very much! 🙇‍♂️ 🙏