docs: 5.x link fixes

[bmorelli25]

Backports the pertinent bits of #1143 to 5.x.

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• Start Time: 2022-01-24T18:39:16.041+0000

• Duration: 11 min 52 sec

• Commit: 28dbe3b

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📦 Bundlesize report

Filename	Size(bundled)	Size(gzip)	Diff(gzip)
elastic-apm-opentracing.umd.min.js	63.4 KiB	20.2 KiB	💚 0 Bytes
elastic-apm-rum.umd.min.js	57.3 KiB	18.7 KiB	💚 0 Bytes