Bug: Text input for /newsletter is broken

[joethreepwood]

Assuming we want to keep this page at all, the text input on /newsletter is broken and won't accept any content.

If we are to keep it then the copy probably needs work on it too, as well as better CTAs across the site @andyvan-ph

Tagging @corywatilo for triage by website team. I had a look, but couldn't figure it out -- and I think @andyvan-ph needs to make the call here too.

[andyvan-ph]

I assume this page is deprecated in favour of the sign-up for on ther blog? In any case, it's probably something we might want to ressurect at some point in the future

[joethreepwood]

It's not deprecated fully - a lot of old blog posts link to it. Basically all the old ones made by Mo.

E.g. https://posthog.com/blog/startup-job-titles

[joethreepwood]

Closing via #3318