UBCL: Add PML/UBCL and OSC/UBCL

[vanman-nguyen]

This PR adds the support for Eviden's communication library, called UBCL (Unified Bxi Communication Layer), by the addition of a PML/UBCL and of an OSC/UBCL, thus enabling MPI communications through the BXI network.
Both components are currently maintained by us.

[github-actions]

Hello! The Git Commit Checker CI bot found a few problems with this PR:

c11e519: UBCL: Add PML/UBCL and OSC/UBCL

• check_cherry_pick: does not include a cherry pick message (did you need to bot:notacherrypick?)

Please fix these problems and, if necessary, force-push new commits back up to the PR branch. Thanks!

[edgargabriel]

@vanman-nguyen code cannot be directly contributed to a release branch. You need to get it first into the main branch. In addition, the general rule is that features are usually not allowed to be added to existing release series, only bug fixes.

[janjust]

I'm echoing @edgargabriel here as well. We have on occasion bent the rules regarding new feature, but to my knowledge only to existing well established components, and for relatively small features. But new features have to go into main first, and once branching happens they are not backported to existing branches.

[edgargabriel]

@vanman-nguyen can you refile your PR against main, and we can bring it over to the 6.0 branch after that?