feat: allow servers and channels to be defined as components

[smoya]

Note that this PR is targeting asyncapi:2022-01-release branch, so merging it won't release a new version.

Description
This PR is part of #660.
It allows both servers and channels to be defined as (and referenced from) components, meaning the following will be now valid:

servers:
  production:
    $ref: '#/components/servers/myserver'
channels:
  some/events:
    $ref: '#/components/channels/myChannel'
components:
  servers:
    myserver:
      url: "http://localhost:5000/ws"
      protocol: ws
  channels:
    myChannel:
      description: "mychannel"

Related issue(s)
#660

[derberg]

@smoya fyi this pr goes to master, not release branch. Also, we release stuff from release branches, we create release candidates that are automatically published to the website. So you should have prefix feat: as you are introducing a feature

FYI, I haven't looked into the proposal itself, just quickly noticed what you wrote when I saw a pop up in slack channel and thought I will give you a quick heads up. For proposals, I plan to delegate some time next week to jump into the review in spec repo

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

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[smoya]

This branch is now up-to-date with 2022-01-release and all conflicts have been solved.
Also, the social media example has been edited to illustrate the changes. As mentioned in #660 (comment):

unfortunately, the only thing it can be moved to components is one of the servers. See the diff here.
The reason for not moving the rest of servers and channels is because some field change, such as the descriptiion and, as per today, our reference and bundling system does not support fields to be overridden (We follow JSON Reference).

cc @derberg

[derberg]

/dnm

[derberg]

All stuff in place, reference implementation provided and will be released to release branches after this merge.

/rtm

[asyncapi-bot]

🎉 This PR is included in version 2.3.0-2022-01-release.2 🎉

The release is available on GitHub release

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