(3/3) Use Zap for structured logging rather than logrus.

[rtrox]

NOTE: this is not actually a particularly large PR, but it depends on #110 and #113. This will be easiest to review after reviewing & merging those PRs, and rebasing this one. In the meantime, you can see just the changes in this PR by viewing this commit.

Description of the change

Per title, replaces Logrus with Zap, and utilizes structured logging for logs. This PR also adds a new flag, --log-format, which allows toggling between Console & JSON logging. Examples of what logging looks like with each:

# --log-format console (default) --log-level debug
2023-03-17T10:54:23.700-0700	DEBUG	Logger initialized
2023-03-17T10:54:23.701-0700	INFO	Starting HTTP Server	{"interface": "0.0.0.0", "port": 8081}
2023-03-17T10:54:28.453-0700	DEBUG	Request Received	{"remote_addr": "[::1]:61839", "method": "GET", "url": "/metrics"}
2023-03-17T10:54:28.454-0700	INFO	Sending HTTP request	{"url": "https://radarr.redact.com/api/v3/rootfolder"}
2023-03-17T10:54:28.454-0700	INFO	Sending HTTP request	{"url": "https://radarr.redact.com/api/v3/history"}
2023-03-17T10:54:28.454-0700	INFO	Sending HTTP request	{"url": "https://radarr.redact.com/api/v3/system/status"}
2023-03-17T10:54:28.454-0700	INFO	Sending HTTP request	{"url": "https://radarr.redact.com/api/v3/queue"}
2023-03-17T10:54:28.455-0700	INFO	Sending HTTP request	{"url": "https://radarr.redact.com/api/v3/health"}
2023-03-17T10:54:28.455-0700	INFO	Sending HTTP request	{"url": "https://radarr.redact.com/api/v3/movie"}
2023-03-17T10:54:28.640-0700	DEBUG	Request Received	{"remote_addr": "[::1]:61839", "method": "GET", "url": "/favicon.ico"}
2023-03-17T10:55:27.465-0700	INFO	Shutting down due to signal: interrupt

# --log-format json --log-format debug
{"level":"debug","ts":1679075648.1925929,"msg":"Logger initialized"}
{"level":"info","ts":1679075648.192713,"msg":"Starting HTTP Server","interface":"0.0.0.0","port":8081}
{"level":"debug","ts":1679075652.173582,"msg":"Request Received","remote_addr":"[::1]:61825","method":"GET","url":"/metrics"}
{"level":"info","ts":1679075652.173814,"msg":"Sending HTTP request","url":"https://radarr.redact.com/api/v3/history"}
{"level":"info","ts":1679075652.173852,"msg":"Sending HTTP request","url":"https://radarr.redact.com/api/v3/rootfolder"}
{"level":"info","ts":1679075652.173957,"msg":"Sending HTTP request","url":"https://radarr.redact.com/api/v3/health"}
{"level":"info","ts":1679075652.173992,"msg":"Sending HTTP request","url":"https://radarr.redact.com/api/v3/system/status"}
{"level":"info","ts":1679075652.174219,"msg":"Sending HTTP request","url":"https://radarr.redact.com/api/v3/movie"}
{"level":"info","ts":1679075652.175252,"msg":"Sending HTTP request","url":"https://radarr.redact.com/api/v3/queue"}
{"level":"debug","ts":1679075652.382421,"msg":"Request Received","remote_addr":"[::1]:61825","method":"GET","url":"/favicon.ico"}
{"level":"info","ts":1679075660.293376,"msg":"Shutting down due to signal: interrupt"}

Benefits

• Maintenance - Logrus has entered maintenance mode, Zap is under active development
• Parseability - Structured logging, especially with a JSON formatter, is significantly easier to parse using log aggregation tools like loki, logstash, or splunk.

Possible drawbacks

Using a new logger comes with a change in logging format.

Applicable issues

• fixes Refactor: Switch to zap logging library #57

Additional information

[rtrox]

Good to go here, too -- validation errors were trying to log before the logger had been configured. Since these need to immediately exit, printing the error directly to stderr.

[onedr0p]

I've reviewed this commit so anytime you're free to rebase we can merge it.

[rtrox]

rebased, we should be all set!

[onedr0p]

I'm going to test out the changes further today and release v2.0.0 soon.