Document minimum required versions

The libraries that opentelemetry-cpp requires have minimum required versions which are higher than the ones that are natively available on the systems being tested. By listing the exact versions of the libraries, the dependencies are clearly stated which removes the guesswork from build problems.

Author: markus456

docs/dependencies.md

@@ -6,6 +6,8 @@ There are
 - Internal dependencies as the part of code from external libraries
   backported/copied in main repo.
 
+The minimum required versions of the third-party libraries that are required can be found in the [third_party_minimum](../install/cmake/third_party_minimum) file. The minimum supported versions are listed here for convenience but the authorative source is always the linked file.
+
 Both these dependencies are listed here:
 
 ## Internal dependencies
@@ -37,7 +39,7 @@ Both these dependencies are listed here:
 
 - [OTLP/HTTP+JSON](/exporters/otlp)
   exporter:
-  - [protobuf](https://github.com/protocolbuffers/protobuf):  Library to
+  - [protobuf](https://github.com/protocolbuffers/protobuf) (v3.21.6 or later):  Library to
     serialize structured data.
     - OTLP messages are constructed as protobuf payloads.
     - `protoc` compiler is used to generate C++ stubs for proto files provided
@@ -48,17 +50,17 @@ Both these dependencies are listed here:
       [here](https://github.com/protocolbuffers/protobuf/blob/master/LICENSE).
       The  code generated by protoc compiler is owned by the owner of `.proto`
       file.
-  - [libcurl](https://curl.se/libcurl/) : the multiprotocol file transfer
+  - [libcurl](https://curl.se/libcurl/) (curl-7_81_0 or later) : the multiprotocol file transfer
     library.
     - Export connects with opentelemetry collector over HTTP protocol using
       libcurl library
     - License: Inspired by `MIT/X` but not same.
       <https://curl.se/docs/copyright.html>
-  - [nlohmann/json](https://github.com/nlohmann/json): JSON for Modern C++.
+  - [nlohmann/json](https://github.com/nlohmann/json) (v3.10.5 or later): JSON for Modern C++.
     - protobuf serialized otlp messages are encoded in JSON format using this
       library.
     - License: `MIT License`
-  - [zlib](https://www.zlib.net/): A Massively Spiffy Yet Delicately
+  - [zlib](https://www.zlib.net/) (v1.2.11 or later): A Massively Spiffy Yet Delicately
     Unobtrusive Compression Library.
     - The `http_client` utilizes zlib to compress the message body and send
       it in gzip format.
@@ -68,7 +70,7 @@ Both these dependencies are listed here:
 - [OTLP/gRPC](/exporters/otlp)
   exporter:
   - `protobuf`  OTLP messages are constructed as protobuf payloads.
-  - [gRPC](https://github.com/grpc/grpc): An RPC library and framework
+  - [gRPC](https://github.com/grpc/grpc) (v1.49.2 or later): An RPC library and framework
     - Exporter communicates with OTLP collector using gRPC transport mechanism.
     - License: `Apache License 2.0`
 
@@ -84,7 +86,7 @@ Both these dependencies are listed here:
 
 - [Prometheus](/exporters/prometheus)
   exporter:
-  - [`prometheus-cpp`](https://github.com/jupp0r/prometheus-cpp) Prometheus
+  - [`prometheus-cpp`](https://github.com/jupp0r/prometheus-cpp) (v1.1.0 or later) Prometheus
     Client Library for Modern C++
     - License: `MIT License`
 
@@ -95,7 +97,7 @@ Both these dependencies are listed here:
 
 - [Opentracing](/opentracing-shim)
   shim:
-  - [`opentracing-cpp`](https://github.com/opentracing/opentracing-cpp)
+  - [`opentracing-cpp`](https://github.com/opentracing/opentracing-cpp) (v1.6.0 or later)
     OpenTracing API for C++
     - A bridge layer implementing the OpenTracing API using the OpenTelemetry API
     - License: `Apache License 2.0`

install/cmake/third_party_minimum

@@ -4,6 +4,8 @@
 # Minimum supported version git tags of third-party dependencies
 # Format: <dependency_name>=<release_git_tag>
 
+# Update docs/dependencies.md whenever the minimum version of a library is modified.
+
 abseil=20220623.2
 zlib=v1.2.11
 curl=curl-7_81_0