Hegelc cleanup

[displague]

Description

• Moves /hegelc to /cmd/hegelc
• Adds environment variables (HEGEL_SERVER, HEGEL_PORT)
• Adds flags (-server, -port)
• changes default hostname to metadata from metadata.packet.net
• default error behavior is Fatal (exit code 1) rather than Panic (exit code 2)
• use grpc.DialContext instead of grpc.Dial
• fixes gocritic warnings about exitAfterDefer

Why is this needed

Fixes: #67

How Has This Been Tested?

ran with -help, env variables set, flags set. Attempted invalid ports and hostnames and got appropriate errors.

How are existing users impacted? What migration steps/scripts do we need?

The default server changes from metadata.packet.net to metadata.

Checklist:

I have:

• updated the documentation and/or roadmap (if required)
• added unit or e2e tests
• provided instructions on how to upgrade

[mmlb]

Note that log.Panic panics and thus defered functions are run, but log.Fatal I think calls os.Exit and does not run defers. I think that's fine though and better for a cli than dumping a stack trace anyway.

[codecov]

Codecov Report

Merging #76 (54c41c0) into main (41e18c1) will not change coverage.
The diff coverage is n/a.

❗ Current head 54c41c0 differs from pull request most recent head 8fe0aed. Consider uploading reports for the commit 8fe0aed to get more accurate results

@@           Coverage Diff           @@
##             main      #76   +/-   ##
=======================================
  Coverage   50.71%   50.71%           
=======================================
  Files           3        3           
  Lines         418      418           
=======================================
  Hits          212      212           
  Misses        175      175           
  Partials       31       31           

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[mmlb]

not a fan of basically empty main, but oh well not really a big deal either