Update conda instructions to use miniforge and conda instead of mambaforge and mamba

[traversaro]

Same motivations as in robotology/robotology-superbuild#1653 .

In a nutshell:

• Since conda 23.10 (released on November 2023), the libmamba solver is the default solver (see https://conda.org/blog/2023-11-06-conda-23-10-0-release/), and that should give more and less the same performances of the mamba command, without the confusion between conda and mamba for new users.
• mambaforge is deprecated since July 2024 and will be removed in January 2025 (see conda-forge/miniforge@362b0c4). As now miniforge also contains mamba, users can just install miniforge in place of mambaforge and get exactly the same functionality.

So this PR changes all the instances of mambaforge to miniforge and of mamba to conda.

Other changes:

• Do not suggest the use of robotology-distro to install all packages. The robotology-distro is just a package that constraint the version of packages to be the one of the corresponding distro, but does not install all packages, for example conda create -n testenv robotology-distro==2024.08.* dones not install yarp, while conda create -n testenv robotology-distro==2024.08.* yarp ensures that yarp==3.9.0 is installed. However, for a long time the package was not built (see https://anaconda.org/robotology/robotology-distro) due to CI problems on releases, so I prefer not to document it as a supported feature (if people want to install version corresponding to a distro, they can manually check https://icub-tech-iit.github.io/documentation/sw_versioning_table/#table, even if it is not super user friendly).
• Explain that some packages are available on conda-forge and other on robotology. As of October 2024, all packages mentioned in the guide (yarp, icub-main, gazebo-yarp-plugins, icub-models) are actually available on conda-forge, however better continue to mention robotology in the instructions in case users try to install some package available only there.

[pattacini]

Thanks!