[web] Optimized images on benchmarks part 1.

...content/docs/benchmarks/creep-after-excavation-bgra/T.png

...tent/docs/benchmarks/creep-after-excavation-bgra/mesh.png

...nchmarks/creep-after-excavation-bgra/stress_xx_yy_110.png

...enchmarks/creep-after-excavation-bgra/stress_xx_yy_20.png

...enchmarks/creep-after-excavation-bgra/stress_xx_yy_50.png

...6_gwf_with_nodal_source_term_analytical_solution_head.png

..._with_nodal_source_term_diff_analytical_solution_head.png

...l_source_term_diff_analytical_solution_head_log_scale.png

web/content/docs/benchmarks/elliptic/drainage_excavation.png

web/content/docs/benchmarks/elliptic/line_1e1_robin_left.png

...t/docs/benchmarks/elliptic/square_1e2_neumann_abs_err.png

...docs/benchmarks/elliptic/square_1e2_neumann_gradients.png

.../benchmarks/elliptic/square_1e2_pcs_0_ts_1_t_1.000000.png

...0000_Pressure_AnalyticalSolution_VolumetricSourceTerm.png

...m_pcs_0_ts_1_t_1.000000_Pressure_VolumetricSourceTerm.png

...diff_Pressure_AnalyticalSolution_VolumetricSourceTerm.png

...erm_Diff_Pressure_AnalyticalSolution_PythonSourceTerm.png

...sson_sin_x_sin_y_sourceterm_Pressure_PythonSourceTerm.png

...erm_Diff_Pressure_AnalyticalSolution_PythonSourceTerm.png

...s/heat-transport-bhe/3D_BHE_GW_advection_figures/mesh.png