[question] [conan2] [config] How do I specify a path containing "~" in global.conf?

### What is your question?

I'm on Conan 2.2.2, trying to find a workaround for conan-io/docs#3732 on Windows. I can bake certificates into a file and then reference it in global.conf.

However, on both Windows and Linux, Conan is very picky about the directory string. It doesn't recognize the meaning of the tilde:
```
core.net.http:cacert_path = ~/.conan2/cacert.pem
```
It also doesn't recognize environment variables:
```
core.net.http:cacert_path = ${HOME}/.conan2/cacert.pem
```
And relative paths don't work either (with both files in the same directory):
```
core.net.http:cacert_path = cacert.pem
```
If I manually type out the full path, then things work:
```
core.net.http:cacert.path = /home/foo/.conan2/cacert.pem
```
But this doesn't make for an easily generalizable system that works out of the box for all devs and CI systems.

I then thought about setting the configuration value from a bash script, letting bash expand the path. But I see that Conan2 no longer supports `conan config set foo=bar`. Between this and conan-io/docs#3732 I'm getting frustrated with the removal of critical features I was using in Conan 1.61.0.

Finally I tried looking into the Jinja2 API to see if I could construct a path that way, using the double-braces templating. But I got lost very quickly in that as I've never used it before.

Windows 10 and Ubuntu 22.04
Conan 2.2.2
gcc and msbuild

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- [X] I've read the CONTRIBUTING guide