Allow accessing the entry id in test files

[k33nice]

Hey, thanks for your work! I think it might be nice to have the ability to access the entry ID inside the hurl test file. E.g.:

#1.hurl
POST /foo
{
  "must_be_unique": {{ENTRY_ID}}
}
---EOF---
#2.hurl
POST /foo
{
  "must_be_unique": {{ENTRY_ID}}
}

Thus, it could be running as hurl --test *.hurl

It seems similar to https://github.com/Orange-OpenSource/hurl/issues/606. But it looks more simple, cuz it already there: https://github.com/Orange-OpenSource/hurl/blob/802d78359f8015e3487918b42621c1cb8bbd1eea/packages/hurl/src/runner/hurl_file.rs#L99

Also, sequential ID can be handier rather than random in some cases.

[fabricereix]

Hello @k33nice , this is a good idea. We could have predefined variables available at runtime. we could access the current entry index with {{self.entry.index}} or {{entry.index}}. We initially though about them to get the current time.

Generating sequential id might also be indeed useful. That might be enough for uniqueness in a test.