[apm docs consolidation] 8.7: Delete moved files, update README

[colleenmcginnis]

Related to #12341

[colleenmcginnis]

@elasticmachine, run elasticsearch-ci/docs

[colleenmcginnis]

The docs build passed. 🤷‍♀️ I'm not familiar with the failing checks.

[carsonip]

diff --git a/NOTICE.txt b/NOTICE.txt
index 30c9e6c0c..51405e382 100644
--- a/NOTICE.txt
+++ b/NOTICE.txt
@@ -1,5 +1,5 @@
 Elastic APM Server
-Copyright 2014-2023 Elasticsearch BV
+Copyright 2014-2024 Elasticsearch BV
 
 This product includes software developed by The Apache Software 
 Foundation (http://www.apache.org/).

8.8 backport PR #12358 is passing CI because there's a shortcut for docs to bypass the lint check #10564 . We either 1. fix the year in NOTICE.txt for all old branches like we did in #12333; or 2. update CI to bypass the check for docs PRs. I like the latter better.

[carsonip]

CI because there's a shortcut for docs to bypass the lint check

actually, the same bypass exists for 8.7 branch, but because there are .yml files deleted in the PR, it triggers the lint job instead of bypassing it.

[bmorelli25]

Is it worth doing that for all of these branches? Or can we just merge this because these are the last docs PRs that will ever go into these branches?

Edit: I'm going to update the notice.txt

[v1v]

run docs-build