add missing openssl system dep to folly

folly is is missing a linux system dep for openssl.  Add one so that install-system-deps knows to install openssl rpms/debs.

openssl getdeps manifest already relies on system openssl on linux so its ok for folly to depend on it


Test plan:

run on a fresh ubuntu 20.04 toolbox which doesn't have openssl already:
```
./build/fbcode_builder/getdeps.py --allow-system-packages install-system-deps --recursive folly
./build/fbcode_builder/getdeps.py --allow-system-packages build --no-tests --src-dir=.  folly
```

Before,  error
```
CMake Error at /usr/share/cmake-3.16/Modules/FindPackageHandleStandardArgs.cmake:146 (message):
  Could NOT find OpenSSL, try to set the path to OpenSSL root folder in the
  system variable OPENSSL_ROOT_DIR (missing: OPENSSL_CRYPTO_LIBRARY
  OPENSSL_INCLUDE_DIR) (Required is at least version "1.1.1")
Call Stack (most recent call first):
  /usr/share/cmake-3.16/Modules/FindPackageHandleStandardArgs.cmake:393 (_FPHSA_FAILURE_MESSAGE)
  /usr/share/cmake-3.16/Modules/FindOpenSSL.cmake:447 (find_package_handle_standard_args)
  CMake/folly-deps.cmake:81 (find_package)
  CMakeLists.txt:144 (include)
```

After, works

.github/workflows/getdeps_linux.yml

@@ -27,6 +27,8 @@ jobs:
       run: sudo python3 build/fbcode_builder/getdeps.py --allow-system-packages install-system-deps --recursive folly
     - name: Fetch boost
       run: python3 build/fbcode_builder/getdeps.py --allow-system-packages fetch --no-tests boost
+    - name: Fetch openssl
+      run: python3 build/fbcode_builder/getdeps.py --allow-system-packages fetch --no-tests openssl
     - name: Fetch ninja
       run: python3 build/fbcode_builder/getdeps.py --allow-system-packages fetch --no-tests ninja
     - name: Fetch cmake
@@ -61,6 +63,8 @@ jobs:
       run: python3 build/fbcode_builder/getdeps.py --allow-system-packages fetch --no-tests xz
     - name: Build boost
       run: python3 build/fbcode_builder/getdeps.py --allow-system-packages build --free-up-disk --no-tests boost
+    - name: Build openssl
+      run: python3 build/fbcode_builder/getdeps.py --allow-system-packages build --free-up-disk --no-tests openssl
     - name: Build ninja
       run: python3 build/fbcode_builder/getdeps.py --allow-system-packages build --free-up-disk --no-tests ninja
     - name: Build cmake

build/fbcode_builder/manifests/folly

@@ -21,25 +21,17 @@ libsodium
 double-conversion
 fmt
 lz4
+openssl
 snappy
 zstd
-# no openssl or zlib in the linux case, why?
+# no zlib in the linux case, why?
 # these are usually installed on the system
 # and are the easiest system deps to pull in.
-# In the future we want to be able to express
-# that a system dep is sufficient in the manifest
-# for eg: openssl and zlib, but for now we don't
-# have it.
-
-# macOS doesn't expose the openssl api so we need
-# to build our own.
-[dependencies.os=darwin]
-openssl
+# In the future we want zlib manifest to handle 
+# this for us like the openssl one already does
 
-# Windows has neither openssl nor zlib, so we get
-# to provide both
+# Windows no zlib, provide it
 [dependencies.os=windows]
-openssl
 zlib
 
 # xz depends on autoconf which does not build on