Prep work for Elasticsearch 8 upgrade

[mrsweaters]

Jira issue link: MOFONETNAV-167

Overview

Updating test suite and removing outdated specs in preparation for Elasticsearch 8 support.

• Use refresh instead of flush where search is expected to be updated
• Drop support for Ruby 2.5 and 2.6
• Add support for Ruby 2.7 and 3.0, build against Ruby 3.1
• Set search_type to query_then_fetch as we no longer support Elasticsearch version < 7.0
• Set include_type_name when fetching the mapping. Will be removed in the next version to support ES version 8.
• Index names automatically use the new timestamp format when creating an index.

QA Instructions

See https://github.com/doximity/doximity/pull/39531