Bump CAF to version 0.18.6

[patszt]

This PR bumps the CAF version to 0.18.6.
Some of the major weird things happening in the review:

• Many config parsing now have .data() added to string_view. This is added because the get_or calls require the last argument (which is now std::string_view) to have a type_id. The type_id requires the type to be serializable. I dind't come up with a good way to deserialize into std::string_view as it doesn't own a buffer. This is why for now i have just used .data(). In CAF 0.19 this is fixed i believe

[dominiklohmann]

First review round: Everything that relates to the build scaffolding and CI. I really like what I'm seeing so far!

[dominiklohmann]

Second part of the review: lsvast.

[dominiklohmann]

Part three: All the builtins.

[dominiklohmann]

Part four: plugins.

[dominiklohmann]

Part five: The test support library libvast_test.

[dominiklohmann]

Part six: FlatBuffers tables.

[dominiklohmann]

Review round seven: About the first half of the libvast; I'm done for the day.

[dominiklohmann]

Round eight: The remainder of libvast.

[dominiklohmann]

I mostly glanced at the tests as the changes were mostly mechanical. Initial testing shows that everything is working, even with an old database.

I would like to see this merged and then roll this out on our testbed for performance testing and to see what we need to tweak with the defaults.

There's one last warning I get when building, and this diff fixes it:

diff --git a/libvast/test/format/arrow.cpp b/libvast/test/format/arrow.cpp
index 54f3bacd9..a92fa5a0b 100644
--- a/libvast/test/format/arrow.cpp
+++ b/libvast/test/format/arrow.cpp
@@ -94,7 +94,8 @@ TEST(arrow IPC read) {
   format::arrow::writer writer;
   writer.out(stream);
   for (auto& slice : zeek_conn_log)
-    writer.write(slice);
+    if (auto err = writer.write(slice))
+      FAIL("failed to write zeek.conn log " << err);
   auto data = stream->Finish().ValueOrDie()->ToString();
   auto in = std::make_unique<std::istringstream>(std::string{data});
   auto options = caf::settings{};

This PR is a fantastic piece of work 🚀

[dominiklohmann]

I just pushed a bunch of things—only action left to do (assuming that CI runs through) is to squash and then merge!