Add global tolerations in charts for all GitLab components

Proposal

Add the possibility to set nodeSelectors (already present) and tolerations globally so that all the charts of GitLab components deploy the dedicated pods on a specified set of nodes.

There is documentation on global nodeSelectors at https://docs.gitlab.com/charts/charts/globals.html#node-selector. However, some charts, i.e. certmanager-issuer , that don't have tolerations.