feature request: add sprig library or other library for templating support

**Why is this needed**: The Grafana templates are low in features, with not fully oddly documented template functions. They are not documented https://grafana.com/docs/grafana/latest/alerting/fundamentals/notifications/templates/ not at https://grafana.com/docs/grafana/latest/alerting/configure-notifications/template-notifications/reference/ , but at https://grafana.com/docs/grafana/latest/alerting/alerting-rules/templating-labels-annotations/ . There are not enough functions for good templating. In particular I am writing grafana alerts where different people have to be tagged on Microsoft Teams depending on if the input label matches a specific regex. It is not possible to `if` match a label with a regex, it is not possible to split a string. **What would you like to be added**: There is sprig library https://masterminds.github.io/sprig/ . Please add it in all templating contexts to be available. **Who is this feature for?** For any programmers that write grafana alerts.