Allow not rendering pages

[clarfonthey]

• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Are you doing the PR on the next branch?
• Have you created/updated the relevant documentation page(s)

Depends on #2407.

render = false

First, this updates the meaning of render = false:

• Entries in the sitemap will not be included (no change)
• Files are not generated to disk (no change)
• Things are written to SITE_CONTENT instead of disk (the big change)

This means that zola serve will still render non-rendered content, although I consider this mostly a benefit to debugging, not an issue. Since zola serve is not intended for anything besides local development, I consider this a reasonable compromise.

The way I actually implemented this change was by simply updating write_content to allow writing to SITE_CONTENT even if it's run under zola build, so that non-rendered pages, sections, and taxonomies can still be accessed, but aren't actually written to disk. This helps ensure that things are more consistent (you don't have to break at the right point in a function) and hopefully things just work how people expect.

Exposure to templates

This was another thing I added after realising that, since render = false doesn't affect creating permalinks at all (and probably shouldn't), it would be nice for templates to be able to detect whether a page/section is rendered so they can avoid linking things. So, templates now have access to the render variable, which is defaulted to true so you can just check page.render, etc.

Explanation

Right now, the reasoning behind render = false for sections is so that people can use get_section or get_page internally without actually rendering pages for things. So, by this logic, ensuring that these rendered pages show up in SITE_CONTENT feels like the most straightforward way of doing things.

[Keats]

Can you split the refactoring in another PR?

[clarfonthey]

Just to clarify, which specific refactorings? I am fine with just merging the first two commits if that's what you mean, or I could modify the latter three commits to remove render = false from pages if that's what you mean.

[Keats]

what does it mean to have a page to organize things?

[clarfonthey]

I'm not quite sure the best way to word things. One example of something I use it for is my CV - I have jobs as different non-rendered pages in a non-rendered section and just output them directly onto the template for the parent section. This way, it's organised into different parts but this doesn't affect the final output.

[Keats]

Basically split the render = false and the rest in 2 different PRs

[clarfonthey]

Alright, I'll just start with the first two commits for now. Those are now #2407.

[clarfonthey]

Going to close this for now, will provide another PR when I come up with a better version.