Merge bitcoin/bitcoin#29230: doc: update -loglevel help to add info to the always logged levels

ec779a2 doc: add unconditional info loglevel following merge of PR 28318 (Jon Atack)

Pull request description:

  Commit ab34dc6 of #28318 was an incomplete version of [`118c756` (#25203)](bitcoin/bitcoin@118c756) from the `Severity-based logging` parent PR.

  Add the missing text to update the `-loglevel` help doc.

  While here, make the help text a little easier to understand.

  Can be tested by running:

  ```
  ./src/bitcoind -regtest -help-debug | grep -A12 loglevel=
  ```

  before
  ```
    -loglevel=<level>|<category>:<level>
         Set the global or per-category severity level for logging categories
         enabled with the -debug configuration option or the logging RPC:
         info, debug, trace (default=debug); warning and error levels are
         always logged.
  ```

  after
  ```
    -loglevel=<level>|<category>:<level>
         Set the global or per-category severity level for logging categories
         enabled with the -debug configuration option or the logging RPC.
         Possible values are info, debug, trace (default=debug). The
         following levels are always logged: error, warning, info.
  ```

ACKs for top commit:
  stickies-v:
    ACK ec779a2

Tree-SHA512: 0c375e30a5a4c168ca7d97720e8c287f598216767afedae329824e09a480830faf8537b792c5c4bb647c68681c287fe3005c62093708ce85624e9a71c8245e42

Author: fanquake

src/init/common.cpp

@@ -31,7 +31,7 @@ void AddLoggingArgs(ArgsManager& argsman)
         ArgsManager::ALLOW_ANY, OptionsCategory::DEBUG_TEST);
     argsman.AddArg("-debugexclude=<category>", "Exclude debug and trace logging for a category. Can be used in conjunction with -debug=1 to output debug and trace logging 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("-loglevel=<level>|<category>:<level>", strprintf("Set the global or per-category severity level for logging categories enabled with the -debug configuration option or the logging RPC: %s (default=%s); warning and error levels are always logged. If <category>:<level> is supplied, the setting will override the global one and may be specified multiple times to set multiple category-specific levels. <category> can be: %s.", LogInstance().LogLevelsString(), LogInstance().LogLevelToStr(BCLog::DEFAULT_LOG_LEVEL), LogInstance().LogCategoriesString()), ArgsManager::DISALLOW_NEGATION | ArgsManager::DISALLOW_ELISION | ArgsManager::DEBUG_ONLY, OptionsCategory::DEBUG_TEST);
+    argsman.AddArg("-loglevel=<level>|<category>:<level>", strprintf("Set the global or per-category severity level for logging categories enabled with the -debug configuration option or the logging RPC. Possible values are %s (default=%s). The following levels are always logged: error, warning, info. If <category>:<level> is supplied, the setting will override the global one and may be specified multiple times to set multiple category-specific levels. <category> can be: %s.", LogInstance().LogLevelsString(), LogInstance().LogLevelToStr(BCLog::DEFAULT_LOG_LEVEL), LogInstance().LogCategoriesString()), ArgsManager::DISALLOW_NEGATION | ArgsManager::DISALLOW_ELISION | ArgsManager::DEBUG_ONLY, 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
     argsman.AddArg("-logthreadnames", strprintf("Prepend debug output with name of the originating thread (only available on platforms supporting thread_local) (default: %u)", DEFAULT_LOGTHREADNAMES), ArgsManager::ALLOW_ANY, OptionsCategory::DEBUG_TEST);