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

Seastar supports both static and dynamic linkage. and in README.md,
we have a command line example 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