Use "stream name" rather than "manifest ID"

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**Is your feature request related to a problem? Please describe.**
The "Manifest ID" has been a Livepeer-specific concept that has seen quite a bit of evolution. In its current form, the manifest ID can be simply seen as a "stream name".

Referring to the "stream name" throughout the codebase and in our documentation may be more intuitive for users [1] who are unfamiliar with the concept of HLS manifests. This makes it easier to for them to get acclimated to the Livepeer technical environment.

[1] Even seasoned video developers don't necessarily immediately make the connection between "manifestID" and "HLS manifest" or "HLS playlist". Even then, it's a bit ambiguous when considering master playlists vs media playlists, etc.

**Describe the solution you'd like**

Start by updating the documentation, program output and any user-facing features (eg, CLI API) to refer to the "stream name" rather than the "manifest ID".

We don't have to do a wholesale replacement of the term within the user-invisible codebase immediately (such as variable names); the renaming can be done gradually as we work on various areas.

**Describe alternatives you've considered**

We can call it a "stream ID". However, I prefer the "stream name" terminology for a few reasons (all of them entirely subjective):

* It's more suggestive of having a user selected name, which can the case.
* Less suggestive of any restrictions, of which there are very few. Eg, one might ask, "what format does this stream ID need to be in?" while this seems less likely with a stream name.

We can also maintain the "manifest ID" terminology. But then a couple levels of exposition probably have to follow. In my head, the conversation goes like this:

**Q:** "What's a ManifestID?"
**A:** It's a stream identifier

**Q:** "What format is the identifier in?"
**A:** Anything you want!

**Q:** "So it's like a stream name?"
**A:** Exactly!

Search the codebase's documentation, program output, CLI, and API surfaces for user-facing uses of “manifest ID” or “ManifestID”. Update those references to “stream name” while leaving user-invisible variable names for later; done means the terminology is consistent across the identified user-facing surfaces.

Written by the indexing model from the issue text.