Bash completion for flags

[mabelzhang]

🎉 New feature

Part of gazebosim/gz-tools#1
Used together with gazebosim/gz-tools#87

Summary

Bash completion, installation, tests.

Test it

$ . install/share/gz/gz.completion
$ ign msg -     
--force-version  --info           --versions       -i
--help           --list           -h               -l

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[codecov]

Codecov Report

Merging #254 (385141e) into ign-msgs5 (57458eb) will increase coverage by 72.33%.
The diff coverage is n/a.

@@              Coverage Diff               @@
##           ign-msgs5     #254       +/-   ##
==============================================
+ Coverage      12.93%   85.27%   +72.33%     
==============================================
  Files            346        9      -337     
  Lines          60130      903    -59227     
==============================================
- Hits            7779      770     -7009     
+ Misses         52351      133    -52218     

Impacted Files	Coverage Δ
include/ignition/msgs/gps_sensor.pb.cc
include/ignition/msgs/magnetometer_sensor.pb.h
include/ignition/msgs/test.pb.cc
include/ignition/msgs/heightmapgeom.pb.h
include/ignition/msgs/pose.pb.cc
include/ignition/msgs/camera_lens.pb.h
include/ignition/msgs/vector2d.pb.h
include/ignition/msgs/undo_redo.pb.cc
include/ignition/msgs/color.pb.h
include/ignition/msgs/camera_info.pb.h
... and 345 more

---

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[chapulina]

LGTM! Pushed 385141e with some final tweaks:

• Always install CLI files, see Detect ign instead of using cmake module to check for ignition-tools #166 and [tracker] Remove ignition-tools cmake check in Ignition software gazebo-tooling/release-tools#472
• Link against filesystem to fix Bionic build

[scpeters]

I think the debian metadata needs to be updated to install the new completion files

• https://build.osrfoundation.org/job/ign-msgs5-debbuilder/174/console

dh_missing: warning: usr/share/gz/gz1.completion.d/msgs5.bash_completion.sh exists in debian/tmp but is not installed to anywhere