feat: autopopulate GCF metadata

[DominicKramer]

Fixes: #91

[ofrobots]

Q: We are special casing cloud functions here. Should we also be doing something for GAE and other managed environments? Note that we already do provide some of this information in the resource field of the LogEntry: https://github.com/googleapis/nodejs-logging/blob/34878be64cb4475e364624c5a5ea86d4f809fcff/src/log.ts#L825-L834

[DominicKramer]

Yes, providing info for GAE would be good too. I was thinking that could be a follow-up PR, but if you think it belongs in this PR, I can add it.

[ofrobots]

It would be good to know what kind of logic we need to add. Secondly, is there a way to put this logic in the common logging library rather than here? I expect the logging-bunyan also needs it.

[DominicKramer]

Yes, I am still investigating what information we should auto-populate from GAE. Yes, putting this in @google-cloud/logging would be better. I'll move this work there.

[DominicKramer]

This needs the functionality of PR #278 to be able to add execution_id support.

[codecov]

Codecov Report

Merging #276 into master will decrease coverage by 1.5%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master     #276      +/-   ##
==========================================
- Coverage   92.15%   90.65%   -1.51%     
==========================================
  Files           6        6              
  Lines         102      107       +5     
  Branches       18       22       +4     
==========================================
+ Hits           94       97       +3     
  Misses          4        4              
- Partials        4        6       +2

Impacted Files	Coverage Δ
src/common.ts	94.23% <66.66%> (-3.65%)	⬇️

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[DominicKramer]

This PR is no longer needed since @google-cloud/logging PR #400 correctly adds metadata, and console.log on GCF can be used to print messages that show up in the GCP Logs Viewer with the execution_id populated.

[ofrobots]

@DominicKramer I thought this PR was about entryMetadata.labels. googleapis/nodejs-logging#400 is about serviceContext.

[DominicKramer]

My mistake, I meant to say @google-cloud/logging PR #436 instead of PR #400.