0.2.4-alt3 - General updates

• added optional Prometheus metrics endpoint #75 by nicholasgibson2
• Update sphinx and elasticsearch-py #74 by nsano-rururu
• apscheduler>=3.3.0 to >=3.3.0,<4.0 #73 by nsano-rururu
• Kibana Discover support kibana 7.12 #72 by nsano-rururu
• allow loading jinja templates from filesystem #70 by drakaru
• Bump jinja2 from 2.10.1 to 2.11.3 dependencies #69 by dependabot
• Fix search syntax on aggregations #68 by ferozsalam
• Remove unused items in alerta from schema.yaml #67 by nsano-rururu
• fix docs slack_timeout #66 by nsano-rururu
• Update documentation for percentage_format_string and alerta_timeout #65 by nsano-rururu
• Bump tox from 3.22.0 to 3.23.0 #64 by nsano-rururu
• Add FAQ documentation #63 by ferozsalam
• Docker test python 3.6 to 3.9 #62 by nsano-rururu
• Remove mention of new alert platforms from the old README #61 by ferozsalam
• Bump coverage from 5.4 to 5.5 #60 by nsano-rururu
• Update README to point to new docs, deprecate old README #59 by ferozsalam
• added docs jira_assignee #58 by nsano-rururu
• added docs slack_parse_override and slack_text_string #57 by nsano-rururu
• Add a default description for TheHive alerts if one isn't provided #55 by ferozsalam
• Update pylint and tox #54 by nsano-rururu
• Kibana Discover support kibana 7.11 #53 by nsano-rururu
• allow alerta_severity to be set dynamically #52 by mostafahussein
• Creates a new rule config parameter that "use_local_time_for_query" #51 by dilaverdemirel