Add a "tag" member to solvers (allow filtering solvers)

[svaiter]

Looking at the benchmark_lasso, there is numerous implementation of some algorithms, such as PGD. The idea would be to be able to filter the solver according to some tag (e.g. "pgd_solver").

In term of user interface, a search field could be added at the top left.

The implementation could be as simple as a list of string for each Solver. Example celer : ["proximal_cd", "working_set", "python"] julia_pgd : ["proximal_gd", "julia"]