Allow for expired certificate

The code throws for an expired certificate, which results in the below
behavior:

1. If BMC starts when the time is invalid (e.g. the date is in 1970),
bmcweb will create a default certificate with hostname `testhost`;

2. In later reboots when BMC get a valid time, the bmcweb loads the
certificate as before. But phosphor-certificate-manager will throw on
this certificate. Then there is no DBus object created for this
certificate (`/xyz/openbmc_project/certs/server/https/1`)

3. Due to the missing DBus object:
 * We will not be able to replace the certificate, e.g. by below
 Redfish URI:
```
 /redfish/v1/CertificateService/Actions/CertificateService.ReplaceCertificate
```
 * When the BMC gets the hostname, bmcweb will generate a new
 self-signed certificate with the hostname and replace it, the
 replacement fails as well.

This commit adds a config option that allows the expired certificate to
be created on DBus and fixes the above issues and it is enabled by
default.

Signed-off-by: Lei YU <yulei.sh@bytedance.com>
Change-Id: Ib02bd686c9bfeb6401b269af20856824647f54c5
diff --git a/config.h.in b/config.h.in
index b363fd3..3d48991 100644
--- a/config.h.in
+++ b/config.h.in
@@ -21,3 +21,6 @@
 
 /* The default name of the authorities list file. */
 inline constexpr char defaultAuthoritiesListFileName[] = "@authorities_list_name@";
+
+/* Whether to allow expired certificates. */
+inline constexpr bool allowExpired = @allow_expired@;