Introduce APP_SECRET to replace SECRETS

[FelixMalfait]

Context

We currently have 4 environment variables to specify our SECRETS in packages/twenty-server/.env:

• ACCESS_TOKEN_SECRET
• LOGIN_TOKEN_SECRET
• REFRESH_TOKEN_SECRET
• FILE_TOKEN_SECRET

We would like to replace those by a unique APP_SECRET env variable and to generate those 4 when needed as:

• ACCESS_TOKEN_SECRET=SHA256({APP_SECRET}+{workspaceId}+"ACCESS")
• LOGIN_TOKEN_SECRET=SHA256({APP_SECRET}+{workspaceId}+"FILE")
• ...

What & How

• Remove those 4 secrets from the code base
• introduce APP_SECRET instead (this needs to be introduced in several places, I would recommend look for ACCESS_TOKEN_SECRET and to mimick it)
• compute accessTokenSecret based on the formula above whenever it's needed