docs: Update join relationship types

[igorlukanin]

No description provided.

[keydunov]

@igorlukanin Do we have a message here that old relationship names are still valid?

[igorlukanin]

@keydunov Yep, here it is:

[hassankhan]

Love it, great job @igorlukanin 💯

[keydunov]

@keydunov Yep, here it is:

Thanks @igorlukanin! Can we add this message to working with joins page too?

[igorlukanin]

@keydunov I'm OK to do it, however, I've also updated that page (see screenshot) to have a link to the Joins page where this message is present. Do you think there would be confusion anyway? (I'd prefer keeping docs as free as possible from duplicate disclaimers, they pile up and reduce readability for new readers.)

[keydunov]

Ok, let's merge without 2nd warning. I think it should be enough, but if we see questions in the community (Slack & Github), we'd need to add more warning messages.