index.lifecycle.parse_origination_date to allow for custom date formats

[faph]

Description

As per these docs: https://www.elastic.co/guide/en/elasticsearch/reference/7.10/ilm-settings.html#_index_level_settings, the parse_origination_date setting allows parsing of dates in index names using formats like 2022.01.31 only.

We would like to move away from using Curator for index management in favor of ILM. In Curator, we would be able to specify the date format like this:

filters:
- filtertype: age
  source: name
  direction: older
  timestring: '%Y-%m'
  unit: days
  unit_count: 360

For example for a month-based index naming scheme.

Would it be possible to support a custom date format for index origination date parsing?

[elasticmachine]

Pinging @elastic/es-data-management (Team:Data Management)

[tortuegenialez]

I second this request, could we have a status on this? Is this something conceivable or should we rather thing about changing the format used in the name of the index?