Missing dependencies for exported CMake targets in installed configuration file

### Steps to reproduce the behavior

* Prepare an environment with required dependencies installed. (I was using Archlinux with dependencies installed using `sudo pacman -Syu bzip2 gcc-libs gflags jemalloc lz4 snappy zlib zstd`)

* Build RocksDB from current master HEAD with the following commands:
```
cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX= -DWITH_BZ2=ON -DWITH_LZ4=ON -DWITH_SNAPPY=ON -DWITH_ZLIB=ON -DWITH_ZSTD=ON -DUSE_RTTI=ON -DWITH_JEMALLOC=ON -DFAIL_ON_WARNINGS=OFF -DPORTABLE=ON -DWITH_BENCHMARK_TOOLS=OFF
cmake --build . --config Release
cmake --install . --config Release
```

* Write a test project with a `CMakeLists.txt` of the following content:

```
cmake_minimum_required(VERSION 3.10 FATAL_ERROR)

cmake_policy(SET CMP0074 NEW)

project(test_proj1)

find_package(RocksDB CONFIG REQUIRED)

add_executable(test1 test1.cpp)
target_link_libraries(test1 RocksDB::rocksdb-shared)
```

* Configure the test project with the following command:

```
cmake -DRocksDB_ROOT= -DCMAKE_BUILD_TYPE=Release
```

### Expected behavior

The test project should be configured successfully without errors

### Actual behavior

CMake reports dependency missing error when configuring the test project:

```
CMake Error at CMakeLists.txt:9 (add_executable):
Target "test1" links to target "JeMalloc::JeMalloc" but the target was not
found. Perhaps a find_package() call is missing for an IMPORTED target, or
an ALIAS target is missing?

CMake Error at CMakeLists.txt:9 (add_executable):
Target "test1" links to target "gflags::gflags" but the target was not
found. Perhaps a find_package() call is missing for an IMPORTED target, or
an ALIAS target is missing?

CMake Error at CMakeLists.txt:9 (add_executable):
Target "test1" links to target "snappy::snappy" but the target was not
found. Perhaps a find_package() call is missing for an IMPORTED target, or
an ALIAS target is missing?

CMake Error at CMakeLists.txt:9 (add_executable):
Target "test1" links to target "ZLIB::ZLIB" but the target was not found.
Perhaps a find_package() call is missing for an IMPORTED target, or an
ALIAS target is missing?

CMake Error at CMakeLists.txt:9 (add_executable):
Target "test1" links to target "lz4::lz4" but the target was not found.
Perhaps a find_package() call is missing for an IMPORTED target, or an
ALIAS target is missing?

CMake Error at CMakeLists.txt:9 (add_executable):
Target "test1" links to target "zstd::zstd" but the target was not found.
Perhaps a find_package() call is missing for an IMPORTED target, or an
ALIAS target is missing?

-- Generating done
CMake Generate step failed. Build files cannot be regenerated correctly.
```

### Additional Info

The root cause seems to be those dependency targets being exported as interface link libraries of rocksdb, as shown in `lib/cmake/rocksdb/RocksDBTargets.cmake`, yet there's no steps in the configuration files to acutallly find those dependencies. I'm not sure about the original intention why the configuration files are designed like so, but I do want to mention that it is intended in CMake that package configuration file should handle dependencies on its own, if package providers want to encapsule package together with its dependencies.