Fix some issues reported by lintian

Fix some issues reported by lintian

• Set upstream metadata fields: Bug-Database, Bug-Submit, Repository-Browse. (upstream-metadata-file-is-missing, upstream-metadata-missing-bug-tracking)
• Update standards version to 4.6.2, no changes needed. (out-of-date-standards-version)

Debdiff

These changes affect the binary packages:

[The following lists of changes regard files as different if they have different names, permissions or owners.]

Files in second set of .debs but not in first

-rw-r--r--  root/root   /usr/lib/debug/.build-id/be/86979936981cdcafadea1a8d1d1eea21247e68.debug

Files in first set of .debs but not in second

-rw-r--r--  root/root   /usr/lib/debug/.build-id/29/78b869733bde7da65011150c8c76523c5b0a9a.debug

No differences were encountered between the control files of package **libignition-msgs-dev**

No differences were encountered between the control files of package **libignition-msgs8-8**

Control files of package libignition-msgs8-8-dbgsym: lines which differ (wdiff format)

• Build-Ids: 2978b869733bde7da65011150c8c76523c5b0a9a be86979936981cdcafadea1a8d1d1eea21247e68

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Build and test logs for this branch can be found at https://janitor.debian.net/lintian-fixes/pkg/ignition-msgs/e3058c95-293a-4d21-acda-37bc686d6b0f.