Simplify script inclusion when using same domain

[cziegeler]

Currently if you want to load the scripts via the same domain, it is required to first set window.RUM_BASE before including the script.
That leads to two script tags being required, first one which sets that value, second one loading the rum script (deferred).
Couldn't we use ``document.currentScript.src` in the scripts instead which (if I understand it correctly) would mean that all other scripts (as well as the POSTs) would be done via the same host as the initial script has been loaded from

[adobe-bot]

🎉 This issue has been resolved in version 2.4.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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