Integrate vcpkg to manage dependencies for all platforms (Windows, Linux, macOS)

### Motivation

Currently we manage dependencies by ourselves:
- When running unit tests in CI, dependencies are installed from the
  Debian package management tool `apt`
- When verifying macOS build, dependencies are installed from the
  Homebrew package manager
- When verifying Windows build, dependencies are installed via vcpkg but
  no versions are specified
- When building pre-built binaries to release, dependencies are
  installed by scripts under `pkg/` directories. These scripts download
  the source code according to `dependencies.yaml` and build

It makes the pre-built binaries never tested except for the simple
manual tests when voting for a new release. As a result, regression like
#363 could happen.

This patch aims at integrating vcpkg to manage dependencies for all
platforms, not only for Windows.

### Modifications

Integrate the CMakeLists.txt with vcpkg by:
1. Introduce vcpkg as a submodule of this project
2. Update `vcpkg.json` to specify dependency versions.
3. Set `CMAKE_TOOLCHAIN_FILE` with the `vcpkg.cmake` in the submodule.

Then, we can simply use `find_package` to find all dependencies and
depend on them via a target like `CURL::libcurl` to have all include
directores and link libraries.

Update the `unit-tests` workflow to verify building the binaries via
vcpkg to test. The README is also updated to show how much simpler to
build with vcpkg now.

### TODO

There are still some tasks that cannot be done by vcpkg:
1. The static library (e.g. `libpulsarwithdeps.a`) that bundles all
   3rd-party dependencies.
2. The pre-built binaries are still built by scripts under `./pkg`
   directory. Specifically, vcpkg does not work with GCC 4.8 so on
   CentOS 7 we still need to build dependencies manually.

So the previous CMakeLists.txt are retained and will be used if
`INTEGRATE_VCPKG` is OFF (by default). They will be removed until the
task above can be done by vcpkg in future.

Author: BewareMyPower

.github/workflows/ci-pr-validation.yaml

@@ -65,40 +65,40 @@ jobs:
     steps:
       - name: checkout
         uses: actions/checkout@v3
+        with:
+          fetch-depth: 0
+          submodules: recursive
 
-      - name: Install deps
-        run: |
-            sudo apt-get update -y &&           \
-                sudo apt-get install -y         \
-                libcurl4-openssl-dev            \
-                protobuf-compiler               \
-                libprotobuf-dev                 \
-                libboost-dev                    \
-                libboost-program-options-dev    \
-                libzstd-dev                     \
-                libsnappy-dev                   \
-                libgmock-dev                    \
-                libgtest-dev
-
-      - name: Install gtest-parallel
+      - name: Build core libraries
         run: |
-          sudo curl -o /gtest-parallel https://raw.githubusercontent.com/google/gtest-parallel/master/gtest_parallel.py 
-
-      - name: CMake
-        run: cmake . -DCMAKE_BUILD_TYPE=Debug -DBUILD_PERF_TOOLS=ON
+          cmake . -DINTEGRATE_VCPKG=ON -DBUILD_TESTS=OFF
+          cmake --build . -j8
 
       - name: Check formatting
-        run: make check-format
+        run: |
+          ./vcpkg/vcpkg format-manifest vcpkg.json
+          if [[ $(git diff | wc -l) -gt 0 ]]; then
+              echo "Please run `./vcpkg/vcpkg format-manifest vcpkg.json` to reformat vcpkg.json"
+          fi
+          make check-format
 
-      - name: Build
+      - name: Build tests
         run: |
-          # Build the libraries first to avoid possible link failures
-          cmake --build . -j8 --target pulsarShared pulsarStatic
+          cmake . -DINTEGRATE_VCPKG=ON -DBUILD_TESTS=ON
           cmake --build . -j8
 
+      - name: Install gtest-parallel
+        run: |
+          sudo curl -o /gtest-parallel https://raw.githubusercontent.com/google/gtest-parallel/master/gtest_parallel.py 
+
       - name: Run unit tests
         run: RETRY_FAILED=3 ./run-unit-tests.sh
 
+      - name: Build perf tools
+        run: |
+          cmake . -DINTEGRATE_VCPKG=ON -DBUILD_TESTS=ON -DBUILD_PERF_TOOLS=ON
+          cmake --build . -j8
+
   cpp20-build:
     name: Build with the C++20 standard
     runs-on: ubuntu-22.04

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "vcpkg"]
+	path = vcpkg
+	url = https://github.com/microsoft/vcpkg.git