[CI] Add action to trigger conda packages "nightly" builds

[olivier-roussel]

Similarly to what is done with regression, we wand to build conda packages of SOFA master at each commit. This action triggers a workflow on conda-ci repo ( https://github.com/sofa-framework/conda-ci/blob/master/.github/workflows/nightly-sofa.yml ), which will build a conda "nightly" package of SOFA master. Currently these packages were build nightly, this explains their "nightly" naming. These packages are therefore not "nightly" builds anymore, and we will rename them accordingly.

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Reviewers will merge this pull-request only if

• it builds with SUCCESS for all platforms on the CI.
• it does not generate new warnings.
• it does not generate new unit test failures.
• it does not generate new scene test failures.
• it does not break API compatibility.
• it is more than 1 week old (or has fast-merge label).