New manual/gpu

[Iximiel]

Description

@GiovanniBussi @gtribello

I have updated the gpu.md file in the new manual with the information on the currently working openacc actions.

I also added some installation instructions, I would keep them there until we have something stabler.
On top of that I modified configure.ac in order to remove it from the scope of #1268 and, mainly, to make easier to setup openacc.

Target release

I would like my code to appear in release v2.11

Type of contribution

• changes to code or doc authored by PLUMED developers, or additions of code in the core or within the default modules
• changes to a module not authored by you
• new module contribution or edit of a module authored by you

Copyright

• I agree to transfer the copyright of the code I have written to the PLUMED developers or to the author of the code I am modifying.

• the module I added or modified contains a COPYRIGHT file with the correct license information. Code should be released under an open source license. I also used the command cd src && ./header.sh mymodulename in order to make sure the headers of the module are correct.

Tests

• I added a new regtest or modified an existing regtest to validate my changes.
• I verified that all regtests are passed successfully on GitHub Actions.

[Iximiel]

@GiovanniBussi @gtribello can you rereun the -doc-mpi-? it has failed with ../src/lib/plumed: error while loading shared libraries: libplumedKernel.so: cannot open shared object file: No such file or directory and I find it strange

[carlocamilloni]

@Iximiel @gtribello @GiovanniBussi this is failing since the last time I merged v2.10 in master, but v2.10 was passing all tests so I do not know which of the changes in v2.10 is givin problems, I do not think is Max code but more the metatensor changes

[Iximiel]

@Iximiel @gtribello @GiovanniBussi this is failing since the last time I merged v2.10 in master, but v2.10 was passing all tests so I do not know which of the changes in v2.10 is givin problems, I do not think is Max code but more the metatensor changes

maybe also these merge should pass trough a PR