feat(rum-core): add serverUrlPrefix config option

[alexbode]

Change hardcoded serverUrlPrefix to passable parameter to evade ad blockers

fixes issue #1078

[apmmachine]

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Build stats

• Start Time: 2021-10-21T04:02:59.959+0000

• Duration: 76 min 34 sec

• Commit: 7372aa9

Test stats 🧪

Test	Results
Failed	0
Passed	1065
Skipped	9
Total	1074

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[vigneshshanmugam]

Looks good, can you add test here - https://github.com/elastic/apm-agent-rum-js/blob/master/packages/rum-core/test/common/apm-server.spec.js and also add docs on the new flag - https://github.com/elastic/apm-agent-rum-js/blob/master/docs/configuration.asciidoc

[vigneshshanmugam]

/test

[bmorelli25]

@elasticmachine, run elasticsearch-ci/docs

[bmorelli25]

jenkins test this please

[bmorelli25]

Thanks, @alexbode !

[vigneshshanmugam]

@alexbode Can you rebase your commits with feat(rum-core): add serverUrlPrefix config option just to make sure the tests get picked up and lint pass.

[apmmachine]

📦 Bundlesize report

Filename	Size(bundled)	Size(gzip)	Diff(gzip)
elastic-apm-opentracing.umd.min.js	63.3 KiB	20.2 KiB	⚠️ 19 Bytes
elastic-apm-rum.umd.min.js	57.2 KiB	18.7 KiB	⚠️ 20 Bytes

[vigneshshanmugam]

LGTM, Thanks 🎉