License server via MPD tags

[dsilhavy]

Is your feature request related to a problem? Please describe.
Content providers should be able to define the license server via MPD using the dashif:laurl tag. From the IOP v5 spec:

DRM systems generally use the concept of license requests as the mechanism for obtaining content keys and associated usage constraints. For DRM systems that use this concept, one or more dashif:Laurl elements should be present under the ContentProtection descriptor, with the value of the element being the URL to send license requests to.

<ContentProtection
	schemeIdUri="urn:uuid:d0ee2730-09b5-459f-8452-200e52b37567"
	value="FirstDRM 2.0">
	<cenc:pssh>
		YmFzZTY0IGVuY29kZWQgY29udGVudHMgb2YgkXBzc2iSIGJveCB3aXRoIHRoaXMgU3lzdGVtSUQ=
	</cenc:pssh>
	<dashif:Authzurl>https://example.com/tenants/5341/authorize</dashif:Authzurl>
	<dashif:Laurl>https://example.com/AcquireLicense</dashif:Laurl>
</ContentProtection>

[dsilhavy]

Implemented as part of #3793 . An example is available here: https://reference.dashif.org/dash.js/nightly/samples/drm/dashif-laurl.html