Support rendering and display of incoming message templates with complex placeholders

[nblumhardt]

Using its experimental support for dotted property names, Serilog can accept:

Log.Information("Hello, {user.salutation} {user.name}", "Dr.", "Zoidberg");

And the Seq sink will convert the dotted names into structures, e.g. {user: {salutation: 'Dr.', name: 'Zoidberg'}}.

Seq 2024.3 only supports the https://messagetemplates.org spec, so when these messages are ingested into Seq, the message template is not rendered correctly into a message, and the Events screen does not show the event in the desired format.

Assuming dotted names move forward in Serilog, Seq should accept and handle these reliably. Note that this needs to take into account how existing apps/plug-ins will deal with this data.

See also serilog/serilog#2063, datalust/serilog-sinks-seq#223