[DOC] Document minimum required versions (open-telemetry#3562)

Author: markus456

docs/dependencies.md

@@ -6,6 +6,11 @@ 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
+authoritative source is always the linked file.
+
 Both these dependencies are listed here:
 
 ## Internal dependencies
@@ -37,8 +42,8 @@ Both these dependencies are listed here:
 
 - [OTLP/HTTP+JSON](/exporters/otlp)
   exporter:
-  - [protobuf](https://github.com/protocolbuffers/protobuf):  Library to
-    serialize structured data.
+  - [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
       by `opentelemetry-proto`.
@@ -48,18 +53,19 @@ 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
-    library.
+  - [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
-    Unobtrusive Compression Library.
+  - [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.
     - License: The library is licensed
@@ -68,7 +74,7 @@ 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`
 
@@ -84,8 +90,8 @@ Both these dependencies are listed here:
 
 - [Prometheus](/exporters/prometheus)
   exporter:
-  - [`prometheus-cpp`](https://github.com/jupp0r/prometheus-cpp) Prometheus
-    Client Library for Modern C++
+  - [`prometheus-cpp`](https://github.com/jupp0r/prometheus-cpp)
+    (v1.1.0 or later): Prometheus Client Library for Modern C++
     - License: `MIT License`
 
 - [ElasticSearch](/exporters/elasticsearch)
@@ -96,6 +102,6 @@ Both these dependencies are listed here:
 - [Opentracing](/opentracing-shim)
   shim:
   - [`opentracing-cpp`](https://github.com/opentracing/opentracing-cpp)
-    OpenTracing API for C++
+    (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