[license] Add SPDX headers for fmt

[license] Add SPDX headers for tinyxml2

[license] Add SPDX headers for doxygen-awesome

[license] Add SPDX headers to installexternal.py

[license] Add SPDX headers to doubleexp integration

[license] partial licensing of doxygen math filter

[license] Add custom MIT license for fmt

[license] Add Zlib license for tinyxml2

[license] Add BSD-2-Clause for doubleexp integration

[license] add CC-BY-4.0 license for code of conduct

[license] reference copyright holder in AUTHORS.md

[linear][pdesolver] Fix dynamic output and add disabling feature

See merge request !3535

Before this commit, the cursor was not moved to the beginning of
the line for the summary report resulting in the update line hanging
around. Now this is fixed and an option similar to the NewtonSolver
is added to disable the dynamic output and only print the summary.

[test][md][1d3d] Add root-soil kernel coupling benchmark cases C1.2a/b

See merge request !3534

Cases are described in Schnepf et al (2020) https://doi.org/10.3389/fpls.2020.00316
Coupling method described in Koch et al (2022), https://doi.org/10.1016/j.jcp.2021.110823

[ci] Merge some small jobs to improve pipeline runtime

See merge request !3532

[example][pnm] Two fixes for the example

See merge request !3530

Update Authors.md for the release of 3.7

See merge request !3528

Fix Path in Release.md

See merge request !3526

[cmake] Fix installation of json.hpp

See merge request !3524

[test][fix] Make name unique so that output failes are not overwritten

See merge request !3521

[linearsolver][fix] Add missing include

See merge request !3520

Fix CMakeLists and parameterlist

See merge request !3518

[doc][fix] Fix group name parameter

See merge request !3517

[example] Fix missing include

See merge request !3515

[bin] Update version requirement on gcc in install script

See merge request !3514

[doxygen] Extend footer with copyright link

See merge request !3512

[doc] Move some documentation from handbook to doxygen

See merge request !3498