grpc: factor out base classes for gRPC based drivers

[alltilla]

TODO:

• fix macOS build
• manually try out all the drivers
• write news entries about the new options
• follow-up using macros in the parser.h files in cfg-helper

For the reviewers:

• It is not trivial which options are gRPC related and which are actual driver specific. I have made a classification myself and factored out what I thought to be common, but please think about it yourselves, while you are reviewing.
• Some features that I classified as gRPC related were not implemented in some drivers, so I added them. Please double check if the newly added features make sense in the drivers.
• Is it the best to statically link the grpc-common target? I thought that dynamic linking would be better but I received a lot of linker warnings about it not being portable. Have I missed something?
• Is there a better way to merge two sets of keywords than defining a macro like GRPC_KEYWORDS? It messes up the cfg-helper :/ gcc -E and a bit of parsing improvement in axosyslog-cfg-helper will be able to handle this.

[github-actions]

This Pull Request introduces config grammar changes

axoflow/8d8eab09d02508dfeddf1cdbc8fae5d783ef3489 -> alltilla/grpc-factor-out-common-classes

--- a/destination
+++ b/destination

 axosyslog-otlp(
+    keep-alive(
+        <empty>
+        max-pings-without-data(<nonnegative-integer>)
+        time(<nonnegative-integer>)
+        timeout(<nonnegative-integer>)
+    )
 )

 bigquery(
+    auth(
+        adc(<empty>)
+        alts(
+            <empty>
+            target-service-accounts(
+                <empty>
+                <string>
+            )
+        )
+        insecure(<empty>)
+        tls(
+            <empty>
+            ca-file(<string>)
+            cert-file(<string>)
+            key-file(<string>)
+        )
+    )
 )

 loki(
+    batch-bytes(<positive-integer>)
+    compression(<yesno>)
 )

 opentelemetry(
+    keep-alive(
+        <empty>
+        max-pings-without-data(<nonnegative-integer>)
+        time(<nonnegative-integer>)
+        timeout(<nonnegative-integer>)
+    )
 )

 syslog-ng-otlp(
+    keep-alive(
+        <empty>
+        max-pings-without-data(<nonnegative-integer>)
+        time(<nonnegative-integer>)
+        timeout(<nonnegative-integer>)
+    )
 )

[OverOrion]

Let me get back to you with answers to your questions / requests.
Overall a solid looking PR, huge kudos for doing the extraction 💯

[alltilla]

diff --git a/modules/grpc/common/Makefile.am b/modules/grpc/common/Makefile.am
index 541ba9f05..5c2cd99c6 100644
--- a/modules/grpc/common/Makefile.am
+++ b/modules/grpc/common/Makefile.am
@@ -3,7 +3,7 @@ include modules/grpc/common/metrics/Makefile.am
 
 if ENABLE_GRPC
 
-noinst_LTLIBRARIES += modules/grpc/common/libgrpc-common.la
+lib_LTLIBRARIES += modules/grpc/common/libgrpc-common.la
 
 GRPC_COMMON_CFLAGS = \
   -I$(top_srcdir)/modules/grpc/common \

causes

*** Warning: Linking the shared library modules/grpc/loki/libloki.la against the loadable module
*** libgrpc-common.so is not portable!
  CXXLD    modules/grpc/otel/libotel_cpp.la
  CXXLD    modules/grpc/otel/libotel.la

*** Warning: Linking the shared library modules/grpc/otel/libotel.la against the loadable module
*** libgrpc-common.so is not portable!
  CXXLD    modules/grpc/bigquery/libbigquery_cpp.la
  CXXLD    modules/grpc/bigquery/libbigquery.la

*** Warning: Linking the shared library modules/grpc/bigquery/libbigquery.la against the loadable module
*** libgrpc-common.so is not portable!

[MrAnno]

I think we shouldn't introduce more dynamic libraries around the gRPC drivers, we already have one (static linking seems more than okay in this specific case).

[alltilla]

Fixed one review finding and rebased to main.

[MrAnno]

Let's ask @mitzkia to check the compatibility of this PR next week (manually or in an automated way).

[alltilla]

rebased to main