Bump current to 8.16

[lcawl]

Do not merge until release day

The following PRs/issues address broken links:

• https://github.com/elastic/kibana/pull/198854
• https://github.com/elastic/cloud/pull/133754
• https://github.com/elastic/search-docs-team/issues/220
• https://github.com/elastic/observability-docs/issues/4479

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[leemthompo]

There's just a couple backports left to merge for https://github.com/elastic/search-docs-team/issues/220 to be all sewn up 🤞