Instrumentation docs: rename files, drop redundant instrumentation qualifier

[chalin]

@cartermp, all of the Java docs are under

• Docs > Instrumentation > Java

That is, they're already under the Instrumentation section, so I'd like to suggest that we simplify the file names by dropping instrumentation. WDYT?

$ cd <into the java-docs folder>
$ ls -l website_docs
total 64
-rw-r--r--  1 chalin  staff   2910 Dec 20 14:00 _index.md
-rw-r--r--  1 chalin  staff   2761 Dec 20 15:02 automatic_instrumentation.md
-rw-r--r--  1 chalin  staff    856 Dec 20 15:02 instrumentation_examples.md
-rw-r--r--  1 chalin  staff  19501 Dec 20 15:05 manual_instrumentation.md

If you agree, then let's apply this new simplified naming convention moving forward.

Updates are needed for:

• Java docs - Java docs: fix redirects and rename files to use site convention #1068
• JS - JS examples: copyedits and file rename #1095
• Go docs
  • Rename manual_instrumentation and add redirects opentelemetry-go#2480
  • Rename exporting_data.md
  • Bring changes into this repo
• Ruby docs
  • [website_docs] fix broken links, copyedits and file renames opentelemetry-ruby#1120
  • Update Ruby docs 2022/02/04 #1098

/cc @austinlparker

[cartermp]

This seems reasonable to me.

[chalin]

It seems like this applies to the Go docs too.

[svrnm]

looks like this is all done 🎉