Mutual Channel Subscriptions [web]

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## Goal

Better connect people to each other (grow channel subscriptions) by providing highly relevant social proof of a channel's relevance to a user.

## What needs to be done

Add a new component to channel pages that indicates that channels you follow also follow the channel you're viewing.

Example:
- I follow Bill and Jack
- Bill and Jack follow Mark
- When viewing Mark's channel page, the new component indicates that Bill and Jack follow Mark

### Dev note
* Side note, but could be a good opportunity to address the padding within the channel side bar. Should be 24px on each side. Currently seems to be close to 40px.

https://feat-2342-vitess-subs.minds.io/api/v3/subscriptions/relational/also-subscribe-to?guid=1003026063363674113

```json
{"count":1,"users":[{"guid":"991441275603390467","type":"user","subtype":false,"time_created":"1561754020","time_updated":false,"container_guid":"0","owner_guid":"0","site_guid":false,"access_id":"2","tags":[],"nsfw":[],"nsfw_lock":[],"allow_comments":false,"name":"minds","username":"minds","language":"en","icontime":"1584740435","legacy_guid":false,"featured_id":false,"banned":"no","ban_reason":false,"website":"","briefdescription":"","gender":"","city":"","merchant":{"service":"stripe","id":"acct_1H5Gs1IM9qkXUyFt"},"boostProPlus":false,"fb":false,"mature":0,"monetized":"","signup_method":false,"social_profiles":[],"feature_flags":false,"programs":[],"plus":false,"hashtags":false,"verified":false,"founder":false,"disabled_boost":false,"boost_autorotate":true,"categories":[],"wire_rewards":null,"pinned_posts":[],"is_mature":false,"mature_lock":false,"last_accepted_tos":1,"opted_in_hashtags":3,"last_avatar_upload":"0","canary":false,"theme":"dark","toaster_notifications":true,"mode":0,"btc_address":"","surge_token":"","hide_share_buttons":true,"allow_unsubscribed_contact":true,"dismissed_widgets":["discovery-disclaimer-2020"],"liquidity_spot_opt_out":0,"thumbs:up:count":"0","thumbs:down:count":"0","thumbs:up:user_guids":[],"thumbs:down:user_guids":[],"did":"did:web:minds.io:minds","chat":true,"urn":"urn:user:991441275603390467","subscribed":true,"subscriber":true,"boost_rating":1,"pro":false,"pro_published":false,"rewards":true,"p2p_media_enabled":false,"is_admin":true,"onchain_booster":0,"email_confirmed":true,"eth_wallet":"0x7f56CcDB9EB55411Efa3b346a5A9f2bf627E1D83","rating":1,"disable_autoplay_videos":false,"yt_channels":[]}]}
```

## QA

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Consideration is given to how the issue will be demoed and tested prior to being deployed
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## UX/Design

- [Desktop](https://www.figma.com/file/2O5bt8y7TOzpuxm3MD8ri4/Channel-%5BWeb%5D?node-id=109%3A11951)
- [Mobile Responsive](https://www.figma.com/file/2O5bt8y7TOzpuxm3MD8ri4/Channel-%5BWeb%5D?node-id=308%3A12264)

## Personas

- Core Minds users
- New Minds users trying to build out their Newsfeed

## Experiments

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Experiments are not required, but it should be made clear if one is expected. If experiments are required, the hypothesis should be outlined.
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## Acceptance Criteria

<!--
Everyone should be able to understand what is expected to be delivered
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- [x] Displays within a channel's sidebar only where there are one or more mutual subscriptions.
- [x] Will not display when a user is viewing their own channel
- [x] Will only display when a user is logged in.
- [x] Will display whether a user is subscribed / not subscribed to a channel.
- [x] Up to two avatars will display.
- [x] Copy: The area here is quite limited so we need to be selective with the language.
  * [1 mutual subscription] @channelA is subscribed
  * [2 mutual subscriptions] @channelA and @channelB are subscribed
  * [3 mutual subscriptions] @channelA, @channelB and 1 other is subscribed
  * [4+ mutual subscriptions] @channelA, @channelB and 2 others are subscribed

## Definition of Ready Checklist

- [x] Definition Of Done (DoD)
- [x] Acceptance criteria
- [x] Weighted
- [x] QA
- [x] UX/Design
- [x] Personas
- [x] Experiments

Story points: 3.0