feat: support user email and name custom headers

[natalian98]

This PR adds support for new custom headers: X-Name and X-Email. They are mapped with kratos identity.traits claims.

[shipperizer]

why are we not allowing completely custom headers via a config parameter in the charm?

this works, but the headers are vetted by us instead of being fully custom

[natalian98]

why are we not allowing completely custom headers via a config parameter in the charm?

this works, but the headers are vetted by us instead of being fully custom

If this was a config option, the end user wouldn't necessarily know how to map the the headers with kratos claims.

You can specify which ones should be returned with the headers parameter (see here)