all: Rename the tool to kdumpst

Big but self-explanatory commit: rename the tool. The name choice was
kdumpst, since it's a tool to enable both kdump and pstore setting, also
it's a silly wordplay with the superlative of kdump, as in "kdumpest".

It's an invasive change (touches most of the files), but should
offer no functional change other than logging messages showing
kdumpst now, instead of kdump, and some filenames.

Notice it doesn't touch documentation, which will be done in
a subsequent commit.

Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>

save-dumps.header

@@ -6,6 +6,7 @@ set -uo pipefail
 #  Copyright (c) 2021 Valve.
 #  Maintainer: Guilherme G. Piccoli <gpiccoli@igalia.com>
 #
-#  This is the kdump/pstore log collector; this script prepares the
-#  collected data and save it in the local disk, in the next successful boot.
+#  This is the kdumpst log collector; this script prepares the
+#  collected data and save it in the local disk, in the first
+#  successful boot after the panic.
 #