install-dependencies.sh: add libunistring-{dev,devel}

Seastar supports both static and dynamic linkage. and for better
performance, we encourage developer to statically link against
Seastar. this means, all of its linkages are statically linked.

if gnutls is statically linked. it would bring into libunistring, See

```
pkg-config --libs --cflags --static gnutls
-I/usr/include/p11-kit-1 -lgnutls -lgmp -lunistring -latomic -lnettle -lhogweed -lgmp -lnettle -ltasn1 -lidn2 -lunistring -lp11-kit
```

in this change, these packages are included in install-dependencies.sh,
so the building system can have access to them when linking Seastar
statically. please note, these packages are not dependencies of
libhwloc-dev or hwloc-devel. Because, in general, distro packacage
guidelines encourage maintainers to package shared library if possible,
and reuse the shared libraries redistributed by the distro whenever
appropriate.

Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>

install-dependencies.sh

@@ -35,6 +35,7 @@ debian_packages=(
     libpciaccess-dev
     libcrypto++-dev
     libboost-all-dev
+    libunistring-dev
     libxml2-dev
     xfslibs-dev
     libgnutls28-dev
@@ -79,6 +80,7 @@ redhat_packages=(
     libxml2-devel
     xfsprogs-devel
     gnutls-devel
+    libunistring-devel
     lksctp-tools-devel
     lz4-devel
     liburing-devel