feat: Update usage of minBufferTime according to the DASH spec

[avelad]

Related to #7602 (comment)

From 23009-1:

The value of the minimum buffer time does not provide any instructions to the client on how long
to buffer the media. The value however describes how much buffer a client should have under
ideal network conditions. As such, MBT is not describing the burstiness or jitter in the network,
it is describing the burstiness or jitter in the content encoding. Together with the BW value, it is
a property of the content. Using the "leaky bucket" model, it is the size of the bucket that makes
BW true, given the way the content is encoded

[tykus160]

Looks ok for me, but let's wait for other opinions.