Simplify datetime parsing

This code as it stands pulls in the full datetime library from boost,
including io, and a bunch of timezone code.  The bmc doesn't make use of
any of this, so we can rely on a much simplified version.

Unfortunately for us, gcc still doesn't implement the c++20
std::chrono::parse[1].  There is a reference library available from [2]
that backports the parse function to compilers that don't yet support
it, and is the basis for the libc++ version.  This commit opts to copy
in the header as-written, under the assumption that we will never need
to pull in new versions of this library, and will move to the std
ersion as soon as it's available in the next gcc version.

This commit simplifies things down to improve compile times and binary
size.  It saves ~22KB of compressed binary size, or about 3%.

Tested: Unit tests pass.  Pretty good coverage.

[1] https://en.cppreference.com/w/cpp/chrono/parse
[2] https://github.com/HowardHinnant/date/blob/master/include/date/date.h

Signed-off-by: Ed Tanous <edtanous@google.com>
Change-Id: I706b91cc3d9df3f32068125bc47ff0c374eb8d87
diff --git a/meson.build b/meson.build
index fcc0d7c..9f22f23 100644
--- a/meson.build
+++ b/meson.build
@@ -348,6 +348,7 @@
 srcfiles_bmcweb = files(
   'redfish-core/src/error_messages.cpp',
   'redfish-core/src/registries.cpp',
+  'redfish-core/src/utils/time_utils.cpp',
   'redfish-core/src/utils/json_utils.cpp',
   'src/boost_asio_ssl.cpp',
   'src/boost_asio.cpp',