Consider adopting more log fields from ECS

[ChrsMark]

ECS comes with a list of the following fields for log signal.
We can consider adding some or all of them to the Otel log's schema.

ECS fields

ECS Field	ECS Description	ECS Level	Otel
log.file.path	Full path to the log file this event came from, including the file name. It should include the drive letter, when appropriate.If the event wasn’t read from a log file, do not populate this field.type: keywordexample: /var/log/fun-times.log	extended	log.file.path
log.level	Original log level of the log event.If the source of the event provides a log level or textual severity, this is the one that goes in log.level. If your source doesn’t specify one, you may put your event transport’s severity here (e.g. Syslog severity).Some examples are warn, err, i, informational.type: keywordexample: error	core	severity_text
log.logger	The name of the logger inside an application. This is usually the name of the class which initialized the logger, or can be a custom name.type: keywordexample: org.elasticsearch.bootstrap.Bootstrap	core
log.origin.file.line	The line number of the file containing the source code which originated the log event.type: longexample: 42	extended	Zap caller
log.origin.file.name	The name of the file containing the source code which originated the log event.Note that this field is not meant to capture the log file. The correct field to capture the log file is log.file.path.type: keywordexample: Bootstrap.java	extended	Zap caller
log.origin.function	The name of the function or method which originated the log event.type: keywordexample: init	extended	Zap caller (?)
log.syslog	The Syslog metadata of the event, if the event was transmitted via Syslog. Please see RFCs 5424 or 3164.type: object	extended
log.syslog.appname	The device or application that originated the Syslog message, if available.type: keywordexample: sshd	extended	APP-NAME
log.syslog.facility.code	The Syslog numeric facility of the log event, if available.According to RFCs 5424 and 3164, this value should be an integer between 0 and 23.type: longexample: 23	extended	FACILITY
log.syslog.facility.name	The Syslog text-based facility of the log event, if available.type: keywordexample: local7	extended	FACILITY
log.syslog.hostname	The hostname, FQDN, or IP of the machine that originally sent the Syslog message. This is sourced from the hostname field of the syslog header. Depending on the environment, this value may be different from the host that handled the event, especially if the host handling the events is acting as a collector.type: keywordexample: example-host	extended	HOSTNAME
log.syslog.msgid	An identifier for the type of Syslog message, if available. Only applicable for RFC 5424 messages.type: keywordexample: ID47	extended	MSGID
log.syslog.priority	Syslog numeric priority of the event, if available.According to RFCs 5424 and 3164, the priority is 8 * facility + severity. This number is therefore expected to contain a value between 0 and 191.type: longexample: 135	extended
log.syslog.procid	The process name or ID that originated the Syslog message, if available.type: keywordexample: 12345	extended
log.syslog.severity.code	The Syslog numeric severity of the log event, if available.If the event source publishing via Syslog provides a different numeric severity value (e.g. firewall, IDS), your source’s numeric severity should go to event.severity. If the event source does not specify a distinct severity, you can optionally copy the Syslog severity to event.severity.type: longexample: 3	extended	SEVERITY
log.syslog.severity.name	The Syslog numeric severity of the log event, if available.If the event source publishing via Syslog provides a different severity value (e.g. firewall, IDS), your source’s text severity should go to log.level. If the event source does not specify a distinct severity, you can optionally copy the Syslog severity to log.level.type: keywordexample: Error	extended	SEVERITY
log.syslog.structured_data	Structured data expressed in RFC 5424 messages, if available. These are key-value pairs formed from the structured data portion of the syslog message, as defined in RFC 5424 Section 6.3.type: flattened	extended	STRUCTURED-DATA
log.syslog.version	The version of the Syslog protocol specification. Only applicable for RFC 5424 messages.type: keywordexample: 1	extended

cc: @AlexanderWert @kaiyan-sheng @mlunadia

[AlexanderWert]

@ChrsMark In OTel, log.level is modeled as the protobuf fields (severity_number and severity_text) for the logs signal. So, not a semantic conventions attribute.

[jsuereth]

Can you denote which of these is (a) already modeled in OTLP logging signal and (b) already copnsidered in this document: https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/logs/data-model-appendix.md