Add and handle enableComments field in callouts API

[ccanos]

As an Alkemio user I want to be able to enable comments separately on each callout

Current implementation

• Only type POST callouts can have comments
• Comments is an entity linked from callout
• When creating a Post callout, the API receives the enableComments flag, but there's no such flag on UpdateCallout mutation, so once created a callout without comments it will never have comments

Acceptance criteria

• All callout types can have comments, enabled or disabled
• Update Callout mutation can enable comments (create the comments entity, matrix room, etc...)
• Disabling comments doesn't destroy the matrix room, it just disables the comments but we don't want to lose them [??]

Additional Context

Areas that will be affected

Callouts