This PR allows migration of legacy GMail inbox users to new OAuth based
inbox
## How to test?
1. Create an inbox from the seed data and set it's IMAP address to
`imap.gmail.com` from the UI
2. Open `rails console` and run the following
```
inbox = Inbox.find(100) # use your inbox id here
channel = inbox.channel
channel.update(email: 'hello@chatwoot.com')
channel.prompt_reauthorization!
```
3. This will show the prompt on the UI. Once you click on Reauthorize,
it should open Google Auth. Reauthroize with the same email address as
used in the inbox and it should start working as usual
### Setting up ENV
```sh
GOOGLE_OAUTH_CLIENT_ID=<some-hash>.apps.googleusercontent.com
GOOGLE_OAUTH_CLIENT_SECRET=<client-secret>
GOOGLE_OAUTH_CALLBACK_URL="http://localhost:3000/omniauth/google_oauth2/callback"
```
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