Feature/profile contexts

[memsharded]

Changelog: Feature: Add context variable to profile jinja2 rendering (can be "build", "host" and None).
Docs: https://github.com/conan-io/docs/pull/XXXX

Close #18375

[AbrilRBS]

So much passing info down, but I can see that this is in fact useful

[AbrilRBS]

Nice idea to test this, I think we should make sure that users understand that the context would have 3 potential values in the docs

[kammce]

I tested memsharded:feature/profile_contexts on my local machine with my profile fragment looked like this:

{% if context == "host" %}

[settings]
build_type=MinSizeRel
os=baremetal
arch=cortex-m3
libc=custom

[options]
*:platform={{ platform }}

{% endif %}

{% if context == "build" %}

[options]
arm-gnu-toolchain/*:fat_lto=False

{% include "default" %}

{% endif %}

and my build command was:

VERBOSE=1 conan build demos -pr:a conan/profiles/v1/stm32f103c8 -pr arm-gcc-12.3

I was checking to see if my toolchain package would recognize the option fat_lto being False (default: True), and remove the -ffat-lto-objects from the arguments. It worked as I intended on my machine.