Add option to CMake for building static libraries

[Bindu-Bhabu]

ROCKSDB creates a STATIC library target reference by default. Modify the cmake so that the STATIC library is also an option just like creating a SHARED library but kept OFF by default.

[rhubner]

Hello @Bindu-Bhabu,

thank you for you PR.

I tested your PR locally and it break our Java builds. I need to add extra parameter -D ROCKSDB_BUILD_STATIC=ON. I considering that previously we always build static library, I think it will be better do use same defaults :

option(ROCKSDB_BUILD_STATIC "Build static versions of the RocksDB libraries" ON)

Radek

[Bindu-Bhabu]

@rhubner , default is updated, Kindly check

[rhubner]

LGTM ✅