Added config generate-csrf-key, to store a CSRF key that survives restarts and works across instances

Without server.csrf.tokens.key, each server process signs CSRF tokens with
a random key of its own, so tokens are lost on a restart and rejected by
other instances. "job-search config generate-csrf-key" stores a new random
32-byte hex key in the configuration file, without printing it. --print
only prints a key, for JOBSEARCH_SERVER_CSRF_TOKENS_KEY or another
instance. An existing key is only replaced with --force, as that
invalidates every issued token, and no key is stored while
JOBSEARCH_SERVER_CSRF_TOKENS_KEY is set, as it would override the file.

internal/cli/config/command.go

@@ -25,6 +25,7 @@ func NewCommand(opts *cli.Options) *cobra.Command {
 	cmd.AddCommand(commandGet(opts))
 	cmd.AddCommand(commandSet(opts))
 	cmd.AddCommand(commandInit())
+	cmd.AddCommand(commandGenerateCSRFKey(opts))
 
 	return cmd
 }