6.8.3 documentation release

[lcawl]

This ticket tracks PRs for the release notes, version bumps, and branch updates that are necessary for the 6.8.3 release. Please link to PRs as they are created.

PRs for docs repo updates

• Updates shared versions & release-state attributes: Updates shared version attributes for 6.8.3 #1146

PRs for product repo version bumps & RNs

• ES doc version bump & release-state: [DOCS] Bump docs version from 6.8.2 to 6.8.3 elasticsearch#46391
• ES RNs: release notes for 6.8.3 elasticsearch#46157 https://www.elastic.co/guide/en/elasticsearch/reference/6.8/release-notes-6.8.3.html
• ES ML RNs: None: https://github.com/elastic/ml-cpp/issues?q=label%3Av6.8.3+is%3Aclosed
• ES Hadoop version bump: Bump version 6.8.3 -> 6.8.4 elasticsearch-hadoop#1345
• ES Hadoop release notes: 6.8.3 Release Notes elasticsearch-hadoop#1344 https://www.elastic.co/guide/en/elasticsearch/hadoop/6.8/release-notes.html
  -[ ] ESS:
  -[ ] ECE:
• APM RNs and version bump: [docs] 6.8.3 release notes apm-server#2684 https://www.elastic.co/guide/en/apm/server/6.8/release-notes-6.8.html
• Uptime version bump: N/A
• Logstash RNs: Release notes draft for 6.8.3 logstash#11118 https://www.elastic.co/guide/en/logstash/6.8/releasenotes.html
• Logstash doc version bump: bump docs to 6.8.3 logstash#11120
• Beats RNs: https://www.elastic.co/guide/en/beats/libbeat/6.8/release-notes-6.8.3.html
• Beats doc version bump: Bump docs version for 6.8.3 beats#13412
• Kibana RNs: [DOCS] 6.8.3 Release Notes kibana#44669 https://www.elastic.co/guide/en/kibana/6.8/release-notes-6.8.3.html

Removes coming[ ] tags
wherever they appear

• Kibana RNs
• ES RNs