Benjamin Tan 0f605b8aae templates: Timestamp: add after, before methods
This allows for more fine-grained control of timestamp formatting, for
example:

```
[template-aliases]
'format_timestamp(timestamp)' = '''
if(timestamp.before("1 week ago"),
  timestamp.format("%b %d %Y %H:%M"),
  timestamp.ago()
)
'''
```

Closes #3782.
2024-10-16 13:46:06 +08:00
..
2024-10-15 16:31:32 +03:00
2024-09-17 18:24:26 +02:00