Add semantic conventions for log record ID (#3047)

Fixes #597

## Changes

- Add a section for "generic attributes" to the log semconv
- Add an attribute `log_record.id` making use of ULID as discussed in
#597

Some additional notes:
- I kept the PR small, so I left out some other potential attributes,
e.g. something for pre-existing ID (like windows event logs) or for
storing the used logging/eventing system or even something like a
"signature" that might be worth discussing, etc.
- I followed the structure of "generic attributes" from the spans
semconv
- I took some of the existing wording from #597 &
https://github.com/open-telemetry/oteps/pull/97#discussion_r421865344 to
describe the field

---------

Signed-off-by: svrnm <neumanns@cisco.com>
Co-authored-by: Joao Grassi <joao@joaograssi.com>
Co-authored-by: jack-berg <34418638+jack-berg@users.noreply.github.com>
Co-authored-by: Tigran Najaryan <4194920+tigrannajaryan@users.noreply.github.com>

semantic_conventions/logs/general.yaml

@@ -0,0 +1,18 @@
+groups:
+  - id: log.record
+    prefix: log.record
+    brief: >
+      The attributes described in this section are rather generic. They may be used in any Log Record they apply to.
+    attributes:
+      - id: uid
+        type: string
+        requirement_level: opt_in
+        brief: >
+          A unique identifier for the Log Record.
+        note: >
+          If an id is provided, other log records with the same id will be considered duplicates and can be removed safely.
+          This means, that two distinguishable log records MUST have different values.
+
+          The id MAY be an [Universally Unique Lexicographically Sortable Identifier (ULID)](https://github.com/ulid/spec),
+          but other identifiers (e.g. UUID) may be used as needed.
+        examples: ["01ARZ3NDEKTSV4RRFFQ69G5FAV"]

specification/logs/semantic_conventions/README.md

@@ -4,6 +4,7 @@
 
 The following semantic conventions for logs are defined:
 
+* [General](general.md): General semantic attributes that may be used in describing Log Records.
 * [Log Media](media.md): Semantic attributes that may be used in describing the source of a log.
 
 The following semantic conventions for events are defined:

specification/logs/semantic_conventions/general.md

@@ -0,0 +1,27 @@
+# General attributes
+
+**Status**: [Experimental](../../document-status.md)
+
+The attributes described in this section are rather generic.
+They may be used in any Log Record they apply to.
+
+<!-- Re-generate TOC with `markdown-toc --no-first-h1 -i` -->
+
+<!-- toc -->
+
+- [General log identification attributes](#general-log-identification-attributes)
+
+<!-- tocstop -->
+
+## General log identification attributes
+
+These attributes may be used for identifying a Log Record.
+
+<!-- semconv log.record -->
+| Attribute  | Type | Description  | Examples  | Requirement Level |
+|---|---|---|---|---|
+| `log.record.uid` | string | A unique identifier for the Log Record. [1] | `01ARZ3NDEKTSV4RRFFQ69G5FAV` | Opt-In |
+
+**[1]:** If an id is provided, other log records with the same id will be considered duplicates and can be removed safely. This means, that two distinguishable log records MUST have different values.
+The id MAY be an [Universally Unique Lexicographically Sortable Identifier (ULID)](https://github.com/ulid/spec), but other identifiers (e.g. UUID) may be used as needed.
+<!-- endsemconv -->