Rename UserContainer to ServingContainer

[ReToCode]

Description

We currently name the "main" container of a KnativeService UserContainer. As all containers, including sidecars, are provided by the user this name is not ideal. We should check if it is feasible to rename it to ServingContainer without breaking our API.

Todo

• Check if UserContainer can be renamed without breaking the API
• If possible, rename all occurrences in pkg
• If possible, rename all occurrences in serving
• If possible, rename all occurrences in docs

[skonto]

ServingContainer sounds like that the container belongs to Serving somehow though.
I would prefer something like "AppContainer", "MainContainer", "PrimaryContainer" wdyth?

[ReToCode]

Hm it is the container that serves the traffic, so I'm also throwing TrafficContainer in here :) Opinions?

@dprotaso @rhuss

[rhuss]

+1 one for what @skonto says; the name should reflect its key characteristics. TrafficContainer depicts it, but without context, it sounds weird and confusing, IMO. I like MainContainer because that's what it is, the MainContainer, all others are sidecar containers. Another option, which kind of is in-between, could be TargetContainer, but I think MainContainer is clear and simple and is an established 'concept'.

[prashantrewar]

Hey @ReToCode, @rhuss, and @skonto, I want to work on this issue.

[NightFury742]

/assign

[asr2003]

/assign

[dprotaso]

/unassign @asr2003

the issue is already assigned to @NightFury742