Implement anisotropic properties_container.

[icui]

Description

Implement anisotropic properties_container.

Issue Number

Closes #251

Checklist

Please make sure to check developer documentation on specfem docs.

[] I ran the code through pre-commit to check style
[] My code passes all the integration tests
[] I have added sufficient unittests to test my changes
[] I have added/updated documentation for the changes I am proposing
[] I have updated CMakeLists to ensure my code builds
[] My code builds across all platforms

[Rohit-Kakodkar]

We will also need to update src/compute_properties.cpp to add elastic isotropic properties during construction of specfem::compute::properties

[lsawade]

LGTM

[lsawade]

We will also need to update src/compute_properties.cpp to add elastic isotropic properties during construction of specfem::compute::properties

Are you doing this as part of this issue, @icui ?
Maybe open another one or mention this in #228.

[icui]

We will also need to update src/compute_properties.cpp to add elastic isotropic properties during construction of specfem::compute::properties

Are you doing this as part of this issue, @icui ? Maybe open another one or mention this in #228.

I'm working on it.

[icui]

We will also need to update src/compute_properties.cpp to add elastic isotropic properties during construction of specfem::compute::properties

Are you doing this as part of this issue, @icui ? Maybe open another one or mention this in #228.

Now updated. I've merged branch issue-250 in order to compile.

[Rohit-Kakodkar]

LGTM