Introduce typed pipeline

[jaronoff97]

Description: Introduces a typed pipeline for the collector. This allows us to really easily construct a list of enabled components.

NOTE! One decision we need to make:

By using a struct like this, we have to figure out how to handle an empty list of processors. I chose to always include it on marshal i.e. if someone has a pipeline configuration like this:

service:
  extensions:
    - oauth2client
  pipelines:
    traces:
      receivers:
        - otlp
      exporters:
        - otlp/auth

we will then unmarshal and remarshal it to be:

service:
  extensions:
    - oauth2client
  pipelines:
    traces:
      receivers:
        - otlp
      processors: []
      exporters:
        - otlp/auth

IMO this is fine and better than the reverse where we set it explicitly to an empty list and then don't remarshal it with that empty list. If someone has a way to make this work both ways, let me know :)

DECISION

From the SIG we decided this is fine, it's only visible to a user in their configmap, but no functionality difference.

Link to tracking Issue(s):

part of #2603

Testing: unit testing

Documentation: n/a

[swiatekm]

LGTM overall, with one question I'd like to answer before we merge.