add option to relocate prefix.

[DerThorsten]

Problem

Let's say we have two machines:

Alice with a homedir: /home/alice
Bob: /home/bob
Bob wants a new env at /home/bob/myenv
but we cannot create conda/mamba envs on bobs machine directly.
So we need to create the env at Alice's machine, zip it and send it to Bob.

So alice tries

• micromamba create -p /home/bob/myenv
  But this does not work because creating /home/bob/myenv on Alice's machine is impossible.

Solution

add relocate-prefix option to the create command.

micromamba create -p /home/alice/myenv --relocate-prefix /home/bob/myenv will create all files at /home/alice/myenv but they are relocated to /home/bob/myenv
st. we can send this to Bob, and on Bob's machine, the env would behave like an env created on his machine.

Tentative "test"

This script creates and env at prefix and uses the relocate-prefix option
to relocate to prefix_relocated.
After micromamba we copy prefix to prefix_relocated

PREFIX=$(pwd)/prefix
RELOCATE_PREFIX=$(pwd)/prefix_relocated
MICROMAMBA=./bld/micromamba/micromamba

$MICROMAMBA create  \
	--prefix $PREFIX \
	--relocate-prefix=$RELOCATE_PREFIX \
	--log-level=2 --yes --verbose \
	python numpy

cp -r $PREFIX $RELOCATE_PREFIX

We then activate the env at prefix_reloacted

micromamba activate $(pwd)/prefix_relocated

this env seems to be valid and python runs fine. The prefix in python is also using the relocated path.

Python 3.11.0 | packaged by conda-forge | (main, Jan 14 2023, 12:26:40) [Clang 14.0.6 ] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> sys.executable
'/Users/thorstenbeier/src/mamba/prefix_relocated/bin/python'
>>> sys.prefix
'/Users/thorstenbeier/src/mamba/prefix_relocated'
>>> import numpy
>>>

Changes required in the review have been implemented