#### ISSUE TYPE
<!--- Pick one below and delete the rest: -->
- Feature Pull Request
##### SUMMARY
<!--- Describe the change, including rationale and design decisions -->
**Add support for Discord:**
This PR,
- adds discord bot
- adds discord notifier
- adds required discord configurations into comm_config.yaml
- adds discordgo module into go.mod
- adds discord configs into all yaml files
<!---
If you are fixing an existing issue, please include "Fixes #nnn" in your
PR comment; and describe briefly what the change does.
-->
<!--- Please list dependencies added with your change also -->
Fixes#97
### Steps For Creation and Integration:
1. Reach https://discordapp.com/developers/applications
2. Create New Application named Botkube and add a bot named **Botkube** into the Application
3. Copy the Application **CLIENT ID** and place it under _Dischord.botid_ in comm-config.yaml
4. Copy Bot **TOKEN** and place it under _Dischord.token_ in comm-config.yaml
5. Generate the URL with suitable permissions using the OAuth2 URL Generator available under OAuth2 section to the add bot to your Discord server
```
https://discordapp.com/oauth2/authorize?&client_id=<YOUR_CLIENT_ID>&scope=bot&permissions=<SET_OF_PERMISSIONS>
```
6. Paste the generated URL in a new tab, select the discord sever to which you want to add the bot and Authorise Bot addition.
7. Create a new channel and/or copy the **CHANNEL ID** of an existing one that you want to use and place it under _Dischord.channel_
```yaml
# Settings for Discord
discord:
enabled: true
token: 'DISCORD_TOKEN' # BotKube Bot Token
botid: 'DISCORD_BOT_ID' # BotKube Application Client ID
channel: 'DISCORD_CHANNEL_ID' # Discord Channel id for receiving BotKube alerts
notiftype: short # Change notification type short/long you want to receive. notiftype is optional and Default notification type is short (if not specified)
```
#### Note: Follow the first 4 mins of this [Video Tutorial](https://youtu.be/8o25pRbXdFw) to understand the process visually.
### Preview:
