Ensure version command runs on all binaries

[ngotchac]

This PR ensures that the version command can be used with all binaries (heimdalld, heimdallcli and bridge).

One issue was that a config file was required in order to run any command (which is now only required when not running the version command).

Another issue was that the BUILD_FLAGS weren't passed to the go build command.

[vcastellm]

LGTM

[codecov-commenter]

Codecov Report

Merging #779 (5ca1c1b) into master (6569fcd) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #779   +/-   ##
=======================================
  Coverage   72.89%   72.89%           
=======================================
  Files          49       49           
  Lines        3508     3508           
=======================================
  Hits         2557     2557           
  Misses        723      723           
  Partials      228      228           

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