Add SCRATCH_PROJECT_DIR key from Miguel Andrés' MR to Autosubmit 3.15

Hello, @dbeltran, @bdepaula, and @isimomun:

I ran into a similar problem as Miguel Andrés, where the structure of the scratch folder in Fugaku does not follow root+account+user. I have an extra folder in between root and account, data. So Autosubmit 3.15 was failing due to the folder not existing.

I saw https://earth.bsc.es/gitlab/es/autosubmit/-/merge_requests/296 and https://earth.bsc.es/gitlab/es/autosubmit/-/issues/912, so I applied Miguel Andrés' commit and made the necessary changes for 3.15.

Even though now it is working in Fugaku, I am not entirely sure if the changes have not broken for all the other platforms. So that would have to be checked before being merged to the 3.15 branch.