Add basic finite element matrices construction in python

[prudhomm]

Fixes #1738

other matrices can be added in the future

skip components

• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes?
• Have you successfully run the Feel++ testsuite with your changes locally?
• Have you written Doxygen comments in your contribution ?

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[prudhomm]

@vincentchabannes the PR is only on the python version, no need to check the toolboxes or mor
some tests/examples have been added

[vincentchabannes]

this is a big constraint, most OS doesn't are to this level.

[prudhomm]

this is not used currently and will be changed

[prudhomm]

this is used only by cmake preset which works only at cmake 3.21.
python codes will move there and the cmakelists,txt will be updated properly

[prudhomm]

it was added by mistake, I can of course lower the version but it has not impact for now except for those using cmake --preset

[vincentchabannes]

So OK, If you are sure that cmake doesn't failed for a basic use (without preset and thus also lower version)

[prudhomm]

the main cmakelist does not add_subdirectory pyfeelpp-all for now (only via preset)