Merge bitcoin#21060: doc: More precise -debug and -debugexclude doc

572fd0f doc: More precise -debug and -debugexclude doc (wodry)

Pull request description:

  I wondered how one could enable debug logging with `-debug=<category>` for multiple categories. Found out solution is to specify that option multiple times for each wanted category.

  This PR documents this behavior and uses the same wording for the same behavior of `-debugexclude=<category>` to make that also clear and stringent.

ACKs for top commit:
  laanwj:
    ACK 572fd0f
  MarcoFalke:
    ACK 572fd0f
  theStack:
    ACK 572fd0f

Tree-SHA512: 8d93db37602fd5ff4247e7c11478e55b99c0e3d47eaa2bb901937805d8f2a466b3a198b713b760981c5411576b74c52e2909c46c6d3f2e0e04215fd521b65cf7

src/init.cpp

@@ -521,9 +521,9 @@ void SetupServerArgs(NodeContext& node)
     argsman.AddArg("-addrmantest", "Allows to test address relay on localhost", ArgsManager::ALLOW_ANY | ArgsManager::DEBUG_ONLY, OptionsCategory::DEBUG_TEST);
     argsman.AddArg("-capturemessages", "Capture all P2P messages to disk", ArgsManager::ALLOW_BOOL | ArgsManager::DEBUG_ONLY, OptionsCategory::DEBUG_TEST);
     argsman.AddArg("-debug=<category>", "Output debugging information (default: -nodebug, supplying <category> is optional). "
-        "If <category> is not supplied or if <category> = 1, output all debugging information. <category> can be: " + LogInstance().LogCategoriesString() + ".",
+        "If <category> is not supplied or if <category> = 1, output all debugging information. <category> can be: " + LogInstance().LogCategoriesString() + ". This option can be specified multiple times to output multiple categories.",
         ArgsManager::ALLOW_ANY, OptionsCategory::DEBUG_TEST);
-    argsman.AddArg("-debugexclude=<category>", strprintf("Exclude debugging information for a category. Can be used in conjunction with -debug=1 to output debug logs for all categories except one or more specified categories."), ArgsManager::ALLOW_ANY, OptionsCategory::DEBUG_TEST);
+    argsman.AddArg("-debugexclude=<category>", strprintf("Exclude debugging information for a category. Can be used in conjunction with -debug=1 to output debug logs for all categories except the specified category. This option can be specified multiple times to exclude multiple categories."), ArgsManager::ALLOW_ANY, OptionsCategory::DEBUG_TEST);
     argsman.AddArg("-logips", strprintf("Include IP addresses in debug output (default: %u)", DEFAULT_LOGIPS), ArgsManager::ALLOW_ANY, OptionsCategory::DEBUG_TEST);
     argsman.AddArg("-logtimestamps", strprintf("Prepend debug output with timestamp (default: %u)", DEFAULT_LOGTIMESTAMPS), ArgsManager::ALLOW_ANY, OptionsCategory::DEBUG_TEST);
 #ifdef HAVE_THREAD_LOCAL