ngx-voms: cache ac validation results across connections

Currently the results of a VOMS AC validation are cached in the context of a connection. Having caching across connection would improve performance. The entry cache validity must be linked to the AC temporal validity.

changed title from [ngx-voms] cache ac validation results across connections to ngx-voms: cache ac validation results across connections

mentioned in commit f3a5d3f3

mentioned in commit eeb99375

added component:ngx-voms label