Add email user property

[geichelberger]

This PR adds an optional user email property; this is useful if Tobira creates the user reference in Opencast via JWT.

There is a bug if the email column contains a null value; I wonder if I made a mistake or if the macro/FieldIndex does not support null values from the database.

thread 'tokio-runtime-worker' panicked at 'error retrieving column 3: error deserializing column 3: a Postgres value was `NULL`', /xyz/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tokio-postgres-0.7.8/src/row.rs:151:25
stack backtrace:
   0: rust_begin_unwind
   1: core::panicking::panic_fmt
   2: tokio_postgres::row::Row::get
             at /xyz/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tokio-postgres-0.7.8/src/row.rs:151:25
   3: tobira::db::util::FieldIndex::of
             at ./src/db/util.rs:150:9
   4: tobira::auth::User::from_session::{{closure}}
             at ./src/auth/mod.rs:268:20
   5: tobira::auth::User::new::{{closure}}
             at ./src/auth/mod.rs:204:21

[LukasKalbertodt]

Thanks for the thorough PR! You had to touch a lot of files and I don't think you missed anything :D

I still don't understand the motivation behind the PR, though. You said "user reference in Opencast via JWT" but... what does that mean? Why is an email address useful in that case? Can you elaborate?

[geichelberger]

I still don't understand the motivation behind the PR, though. You said "user reference in Opencast via JWT" but... what does that mean? Why is an email address useful in that case? Can you elaborate?

In our setup, if the user gets in touch with our system for the first time via Tobira, the user reference is created with the data from Tobiras JWT Token, and because it does not contain the email address, a dummy one is built like in the docs example.

With a valid email address, sending emails via workflows is possible, and I like consistent data ;).

Seems related to #672

[LukasKalbertodt]

Yeah that makes sense! With my inline comments fixed, this PR can be merged!

[geichelberger]

I removed the email from the user jose for easier testing.

[LukasKalbertodt]

Just one tiny thing!

[LukasKalbertodt]

Thanks a lot!