Add "why rez" doc page

[brycegbrazen]

As a user of rez, I'd like to know more "why" I should use rez vs other package managers. Perhaps we should have a whole new documentation page for this.

Motivation
This will help more users understand what hole rez is filling and if rez meets their needs.

Related Issues/PRs

• https://academysoftwarefdn.slack.com/archives/C0321B828FM/p1710591158400339

[MrLixm]

I agree that we are missing some abstract concepts in the documentation and it would be great to have this !
However, on the "why rez" I think that the welcome page explains pretty explicitly that rez main design is to have a central repository.
So I think the request for this issue should be a bit more specific:

• features of rez (bullet list that is quicker than reading basic concepts)
• what is a package manager (could be the place to introduce the distinction with an environment manager)
• what rez is missing ?
• and we could even add other alternative to rez (I remember the Spack article from Chad Dombrova)

What do you think ?

[maxnbk]

I think we could benefit from a rather extensive and explicit set of "direct comparisons" between rez and other package managers. A lot of people coming to the project are going to be asking "Why don't I just use pip", "Why not conda", "Why not just use your system package manager", and while the questions are obvious, the answers are often non-obvious to people who don't explicitly have the same problem with package management that VFX Studios have.

As well, somewhere, I think that delineating the scope of rez by specifically calling out "configuring what your rez-requests actually are", would be helpful, and I'd hope a future working-subgroup could point to some recommendations for "what to do to manage your rez requests", etc.