feat: make log file path optional and configurable

[jawnsy]

New help output:

$ go run ./cmd/coder/main.go agent start --help
starts the coder agent

Usage:
  coder agent start --coder-url=<coder_url> --token=<token> --log-file=<path> [flags]

Examples:
# start the agent and use CODER_URL and CODER_AGENT_TOKEN env vars
coder agent start

# start the agent and connect with a specified url and agent token
coder agent start --coder-url https://my-coder.com --token xxxx-xxxx

# start the agent and write a copy of the log to /tmp/coder-agent.log
# if the file already exists, it will be truncated
coder agent start --log-file=/tmp/coder-agent.log


Flags:
      --coder-url string   coder access url
  -h, --help               help for start
      --log-file string    write a copy of logs to file
      --token string       coder agent token

Global Flags:
  -v, --verbose   show verbose output

Log to file:

$ go run ./cmd/coder/main.go agent start --log-file=/tmp/file.log
2021-09-02 19:23:22.255 [INFO]  <agent.go:100>  starting wsnet listener {"coder_access_url": "https://master.cdr.dev/"}
2021-09-02 19:23:22.256 [INFO]  <listen.go:114> connecting to broker    {"broker_url": "wss://master.cdr.dev/api/private/envagent/listen?service_token=6067852b-35c4615f433d6b14ede7d1cb"}
2021-09-02 19:23:22.343 [INFO]  <listen.go:136> broker connection established
^C2021-09-02 19:23:23.100 [INFO]        <agent.go:106>  closing wsnet listener
2021-09-02 19:23:23.101 [INFO]  <listen.go:451> listener closed
$ cat /tmp/file.log
2021-09-02 19:23:22.255 [INFO]  <agent.go:100>  starting wsnet listener {"coder_access_url": "https://master.cdr.dev/"}
2021-09-02 19:23:22.256 [INFO]  <listen.go:114> connecting to broker    {"broker_url": "wss://master.cdr.dev/api/private/envagent/listen?service_token=6067852b-35c4615f433d6b14ede7d1cb"}
2021-09-02 19:23:22.343 [INFO]  <listen.go:136> broker connection established
2021-09-02 19:23:23.100 [INFO]  <agent.go:106>  closing wsnet listener
2021-09-02 19:23:23.101 [INFO]  <listen.go:451> listener closed

Permission error:

$  go run ./cmd/coder/main.go agent start --log-file=/tmp/agent.log
2021-09-02 19:23:39.338 [WARN]  <agent.go:64>   failed to open log file {"error": "open /tmp/agent.log: permission denied"}
2021-09-02 19:23:39.339 [INFO]  <agent.go:100>  starting wsnet listener {"coder_access_url": "https://master.cdr.dev/"}
2021-09-02 19:23:39.339 [INFO]  <listen.go:114> connecting to broker    {"broker_url": "wss://master.cdr.dev/api/private/envagent/listen?service_token=6067852b-35c4615f433d6b14ede7d1cb"}
2021-09-02 19:23:39.423 [INFO]  <listen.go:136> broker connection established
^C2021-09-02 19:23:40.226 [INFO]        <agent.go:106>  closing wsnet listener
2021-09-02 19:23:40.226 [INFO]  <listen.go:451> listener closed

exit status 1

Default behavior (no log):

$ go run ./cmd/coder/main.go agent start 
2021-09-02 19:24:39.147 [INFO]  <agent.go:100>  starting wsnet listener {"coder_access_url": "https://master.cdr.dev/"}
2021-09-02 19:24:39.148 [INFO]  <listen.go:114> connecting to broker    {"broker_url": "wss://master.cdr.dev/api/private/envagent/listen?service_token=6067852b-35c4615f433d6b14ede7d1cb"}
2021-09-02 19:24:39.231 [INFO]  <listen.go:136> broker connection established
^C2021-09-02 19:24:40.906 [INFO]        <agent.go:106>  closing wsnet listener

[shortcut-integration]

This pull request has been linked to Clubhouse Story #16783: Modify the coder-cli agent to save to a log as well as stderr.

[coveralls]

Pull Request Test Coverage Report for Build 1195483293

• 7 of 22 (31.82%) changed or added relevant lines in 1 file are covered.
• 6 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.1%) to 47.88%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
internal/cmd/agent.go	7	22	31.82%

Files with Coverage Reduction	New Missed Lines	%
wsnet/dial.go	6	77.07%

Totals
Change from base Build 1194900284:	-0.1%
Covered Lines:	2789
Relevant Lines:	5825

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💛 - Coveralls