`micromamba` paths

[Hind-M]

From y-mamba-reporter in prefix discord:

• Micromamba 2 shell activation puts non-existent dirs on Linux $PATH. It should check that dirs exist before adding them to $PATH. One line at fault is export PATH="${MAMBA_ROOT_PREFIX}/condabin:${PATH} where condabin does not exist here. I have $MAMBA_ROOT_PREFIX/bin holding micromamba itself, and my own login profile scripts already place it on $PATH and define $MAMBA_EXE. My base environment is otherwise empty.

• I also had a bothersome libmamba error message and made an empty $MAMBA_ROOT_PREFIX/conda-meta dir just to stop it (fixed in #3513).

• Lastly, I named $MAMBARC as 'condarc' because micromamba seems to prefer conda names (I'm not sure).

[Hind-M]

* Lastly, I named `$MAMBARC` as 'condarc' because `micromamba` seems to prefer `conda` names (I'm not sure).

There is actually a precedence order regarding the different configuration possibilities (cf. schema and list in https://mamba.readthedocs.io/en/latest/user_guide/configuration.html#multiple-rc-files). So $MAMBARC is supposed to have the highest precedence after CLI configuration. To make sure there is no issue or bug, can you specify your use case and what made you think that micromamba seems to prefer conda names?