shell-completion: support -i option for journalctl

Follow-up for dde54b8a8578cecb3ce90e56aeeaf749dd9e1058.

TODO

@@ -133,7 +133,8 @@ Features:
 * systemd-nspawn: something like --volatile= but that isn't volatile, but
   stores the data in some separate dir on disk. Usecase: keep always up-to-date
   DDIs of some OS in your home dir, but combine its /usr/ with a locally
-  maintained root fs in a regular dir to maintain local state.
+  maintained root fs in a regular dir to maintain local state. (idea: call it
+  --mutable= and take dir or DDI and merge in)
 
 * maybe rework systemd-modules-load to be a generator that just instantiates
   modprobe@.service a bunch of times

shell-completion/bash/journalctl

@@ -48,7 +48,7 @@ _journalctl() {
                       --utc -x --catalog --no-full --force --dump-catalog
                       --flush --rotate --sync --no-hostname -N --fields
                       --list-namespaces --list-invocations -I -v --verbose'
-        [ARG]='-b --boot -D --directory --file -F --field -t --identifier
+        [ARG]='-b --boot -D --directory -i --file -F --field -t --identifier
                       -T --exclude-identifier --facility -M --machine -o --output
                       -u --unit --user-unit -p --priority --root --case-sensitive
                       --namespace --invocation'
@@ -73,7 +73,7 @@ _journalctl() {
                 comps=$(compgen -d -- "$cur")
                 compopt -o filenames
                 ;;
-            --file)
+            --file|-i)
                 comps=$(compgen -f -- "$cur")
                 compopt -o filenames
                 ;;

shell-completion/zsh/_journalctl

@@ -73,7 +73,7 @@ _journalctl_namespaces() {
 # Build arguments for "journalctl" to be used in completion.
 # Use both --user and --system modes, they are not exclusive.
 local -a _modes; _modes=(--user --system)
-local -a _modes_with_arg; _modes_with_arg=(--directory -D --file -M --machine --root)
+local -a _modes_with_arg; _modes_with_arg=(--directory -D -i --file -M --machine --root)
 typeset -a _sys_service_mgr
 local w k v i=0 n=$#words
 while (( i++ < n )); do
@@ -132,7 +132,7 @@ _arguments -s \
     '(--directory -D -M --machine --root --file)'{-M+,--machine=}'[Operate on local container]:machines:_sd_machines' \
     '(--directory -D -M --machine --root --file)'{-D+,--directory=}'[Show journal files from directory]:directories:_directories' \
     '(--directory -D -M --machine --root --file)--root=[Operate on catalog hierarchy under specified directory]:directories:_directories' \
-    '(--directory -D -M --machine --root)*--file=[Operate on specified journal files]:file:_files' \
+    '(--directory -D -M --machine --root)*'{-i+,--file=}'[Operate on specified journal files]:file:_files' \
     '--disk-usage[Show total disk usage]' \
     '--dump-catalog[Dump messages in catalog]' \
     '--flush[Flush all journal data from /run into /var]' \