Allow builds to define their custom condarc to be used

This MR implements the last bit of requirements to tackle bob/bob.conda#71.

You can now specify your own condarc on the root of the directory or at recipe directory to override the default.

Files with name condarc-<branch> have priority.

enabled an automatic merge when the pipeline for 759e9305 succeeds

merged

mentioned in commit 2dc9bac8