Add CMake support for spdlog

This introduces spdlog as an optional dependency.
9 jobs for feature/support_spdlog in 11 minutes and 9 seconds (queued for 5 seconds)
latest
Status Job ID Name Coverage
  Test
passed #164218
duneci
debian-11-gcc-9-17-python

00:05:08

passed #164214
duneci
debian:10 clang-7-libcpp-17

00:06:35

passed #164212
duneci
debian:10 gcc-7-17

00:07:00

passed #164217
duneci iset:avx
debian:10 gcc-7-17--expensive

00:11:07

passed #164211
duneci
debian:10 gcc-8-noassert-17

00:09:18

passed #164210
duneci
debian:11 gcc-9-20

00:07:16

passed #164216
duneci
ubuntu:18.04 clang-5-17

00:06:42

passed #164215
duneci
ubuntu:18.04 clang-6-17

00:07:03

passed #164213
duneci
ubuntu:20.04 clang-10-20

00:04:21