cmds.secrets.CmdCompileTemplates: Support -k / --keep-going

jw-pkg secrets compile-templates iterates over all selected templates and
compiles secrets from it - unless it encounters one that can't be compiled
for whatever reason, in which case the iteration errors out without
compiling the remaining secrets.

Add a -k / --keep-going option that makes the iteration not abort over
failed compilations but continue through the remaining templates, then
report an error status at the end.

The integration test gains a good sibling of the failing fixture template:
a fail-fast run must not reach it, and a keep-going run must compile it and
still fail the command.

Signed-off-by: Jan Lindemann <jan@janware.com>
Assisted-by: unsloth/Qwen3.8-27B-GGUF:Q4_K_M with pi.dev v1.4.0

test/integration/jw_pkg/help/test-expected.txt

@@ -848,7 +848,7 @@ Available subcommands of secrets:
     rm-compilation-output
                         Remove package compilation output files
 ============= Running: jw-pkg.py -t ../../../.. --log-level info secrets compile-templates --help
-usage: jw-pkg.py secrets compile-templates [-h] [--owner OWNER]
+usage: jw-pkg.py secrets compile-templates [-h] [--keep-going] [--owner OWNER]
                                            [--group GROUP] [--mode MODE]
                                            [packages ...]
 
@@ -859,6 +859,8 @@ positional arguments:
 
 options:
   -h, --help         show this help message and exit
+  --keep-going, -k   Compile all templates, reporting the failures at the end
+                     (default: False)
   --owner, -o OWNER  Default output file owner (default: None)
   --group, -g GROUP  Default output file group (default: None)
   --mode, -m MODE    Default output file mode (octal) (default: None)