[Draft] etcd: Support configuring zap console log format with --log-format flag

[serathius]

Console format is much easier to read during development when compared
to json.

Example:

2021-05-14T12:11:46.513+0200    info    etcdmain/etcd.go:72     Running:        {"args": ["./bin/etcd", "--log-format=console"]}
2021-05-14T12:11:46.514+0200    warn    etcdmain/etcd.go:104    'data-dir' was empty; using default     {"data-dir": "default.etcd"}
2021-05-14T12:11:46.514+0200    info    etcdmain/etcd.go:115    server has been already initialized     {"data-dir": "default.etcd", "dir-type": "member"}
2021-05-14T12:11:46.514+0200    info    embed/etcd.go:131       configuring peer listeners      {"listen-peer-urls": ["http://localhost:2380"]}
2021-05-14T12:11:46.515+0200    info    embed/etcd.go:139       configuring client listeners    {"listen-client-urls": ["http://localhost:2379"]}

Please read https://github.com/etcd-io/etcd/blob/master/CONTRIBUTING.md#contribution-flow.

[serathius]

cc @ptabor

[codecov-commenter]

Codecov Report

Merging #12967 (fc0956c) into main (7ba53c7) will increase coverage by 6.24%.
The diff coverage is 77.77%.

@@            Coverage Diff             @@
##             main   #12967      +/-   ##
==========================================
+ Coverage   62.73%   68.97%   +6.24%     
==========================================
  Files         417      410       -7     
  Lines       33332    33651     +319     
==========================================
+ Hits        20910    23212    +2302     
+ Misses      10338     8483    -1855     
+ Partials     2084     1956     -128     

Flag	Coverage Δ
all	68.97% <77.77%> (+6.24%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
server/embed/config_logging.go	74.00% <33.33%> (+24.67%)	⬆️
server/embed/config.go	71.00% <100.00%> (+25.31%)	⬆️
server/etcdmain/config.go	83.19% <100.00%> (+2.94%)	⬆️
raft/quorum/quorum.go	0.00% <0.00%> (-100.00%)	⬇️
raft/tracker/state.go	0.00% <0.00%> (-100.00%)	⬇️
raft/util.go	22.42% <0.00%> (-63.56%)	⬇️
raft/confchange/restore.go	39.53% <0.00%> (-55.82%)	⬇️
raft/raftpb/confchange.go	22.97% <0.00%> (-52.71%)	⬇️
raft/quorum/voteresult_string.go	0.00% <0.00%> (-50.00%)	⬇️
raft/logger.go	15.38% <0.00%> (-42.31%)	⬇️
... and 179 more

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[serathius]

Discussed with @ptabor how we want to approach adding new configuration flags. We will go with same approach as log rotation, allowing users to pass full zap config as JSON. #12774 (comment)

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed after 21 days if no further activity occurs. Thank you for your contributions.