Add cmake option to switch parameters and geometry to mcbm fork.

Enabled switching to mcbm forks via:

cmake -DCBM_MCBM_PARS=ON build

And to switch back:

cmake -DCBM_MCBM_PARS=OFF build

@p.-a.loizeau, marked this as draft because I'm not sure this is something we even want. Certainly makes things easier for me to generate the online setups from these forks. But I'd much rather figure out how we can get rid of these forks.

added Build System Externals Parameters mCBM labels

requested review from @p.-a.loizeau

assigned to @p.-a.loizeau

added 5 commits

• 4789174d...a019ba37 - 4 commits from branch computing:master
• 5d8fd3da - Add cmake option to switch parameters and geometry to mcbm fork.

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Dear @f.uhlig,

you have been identified as code owner of at least one file which was changed with this merge request.

Please check the changes and approve them or request changes.

added CodeOwners label

marked this merge request as ready

added 13 commits

• 5d8fd3da...0c78dccb - 12 commits from branch computing:master
• 87372303 - Add cmake option to switch parameters and geometry to mcbm fork.

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merged