Sendmailer configuration should allow non-emails as username for SendGrid

[alexacron]

Bug report

Sendgrid requires "apikey" as username

Issue Description

Their system uses the static string "apikey" as username and the API key as password. Your form requires "email" as username in the configuration form here: /en/member/settings/swiftmailer/update/{mailername}

Preconditions

Latest requirements:

1. framework: latest.
2. php 7.3.

Steps to reproduce

1. edit swiftmailer settings for sendgrid: server: smtp.sendgrid.net, port 465, encryption ssl, auth mode: login, sender Address: a verified account
2. use "apikey" (exactly as typed, 6 letters, lowercase, a,p,i,k,e,y) as per their documentation. API key as password
3. save. Will rise a validation error, "email is not valid"

Expected result

**It should allow using simple strings as username, not emails. **

Actual result

Using @ will allow saving but sending emails fails

Patch until there will be a solution

** Modify config/packages/uvdesk.yaml so it reads "apikey" as username