Support Expression templating for custom Links

# Summary

The templating system for the Links could be improved to support:
- keys containing special characters
- usage of functions

The templating system for the links would work the same way as the Expression templating system for the Workflows (https://argoproj.github.io/argo-workflows/variables/#expression).

# Use Cases

Usage of keys containing special characters would be useful if I want to use a workflow metadata like `workflows.argoproj.io/workflow-template` in a Link.

The usage of functions would allow the modification of the fields. For example, I would like to add a few seconds to `status.finishedAtEpoch` to take into account the Promtail scrap delay. This could also be useful for formatting, trimming, etc.

---

**Message from the maintainers**:

Love this enhancement proposal? Give it a 👍. We prioritise the proposals with the most 👍.

The issue names no files or tests. Start by comparing custom Links templating with the Expression templating system for Workflows described in the linked documentation; done means Links support keys containing special characters and function-based modifications such as adding time or formatting values.

Written by the indexing model from the issue text.