Add rake task to enable the elasticsearch slow log

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Background

Slowlog is currently enabled manually using change requests. This doesn't scale and the team needs to automate this.

Proposal

• Add a new rake task (see elastic rake tasks and Search::Elastic::RakeTaskExecutor service) to enable the slowlog for all indices. The task should:
  • return early if the slowlog is enabled already
  • allow indices to be chosen (so only some could have it enabled)
  • enable the slowlog with a specific setting on each index
  • support both Elasticsearch and OpenSearch, research if there are differences in enable slowlog on both
• Add specs for the task
• Add task to advanced search admin docs