[configuration] Specify YAML schema that configuration files should follow (#3973)

Fixes #3962

## Changes

Specifies the YAML schema to follow. A schema is a set of YAML tags
(i.e. types) and a way to assign types.

YAML 1.2 recommends the 'Core schema': the types are those of JSON.
Scalars are resolved as one would expect, see
[here](https://yaml.org/spec/1.2.2/#103-core-schema) for the details.

One important difference with the way that YAML 1.1 used to work is that
integer scalars starting with a `0` are interpreted as being written in
decimal notation; e.g. `0123` parses to the integer 123 instead of the
integer 83 (you can still use octal notation in YAML 1.2 by using
`0o123`). Some YAML parsers deviate from the core schema in how this
works, for example, both of the more commonly used YAML parsing
libraries in Golang parse `0123` as 83
([go-yaml/yaml](https://github.com/go-yaml/yaml?tab=readme-ov-file#compatibility)
and
[goccy/go-yaml](https://github.com/goccy/go-yaml/blob/4653a1bb5c0047bb37280ac341e2f091cb44352f/ast/ast.go#L326)).
**This may make it a bit difficult to strictly follow this requirement
in some languages**.

For non-trivial changes, follow the [change proposal
process](https://github.com/open-telemetry/opentelemetry-specification/blob/main/CONTRIBUTING.md#proposing-a-change).

* [x] Related issues #3962, part of #3963

---------

Co-authored-by: Robert Pająk <[email protected]>
Co-authored-by: jack-berg <[email protected]>

Author: 3 people

CHANGELOG.md

@@ -46,6 +46,8 @@ release.
   ([#4002](https://github.com/open-telemetry/opentelemetry-specification/pull/4002))
 - Add end to end examples for file configuration
   ([#4018](https://github.com/open-telemetry/opentelemetry-specification/pull/4018))
+- Clarify the schema for YAML configuration files
+  ([#3973](https://github.com/open-telemetry/opentelemetry-specification/pull/3973))
 
 ### Common
 

specification/configuration/file-configuration.md

@@ -65,6 +65,8 @@ Configuration files SHOULD use one the following serialization formats:
 [YAML](https://yaml.org/spec/1.2.2/) configuration files SHOULD follow YAML spec
 revision >= 1.2.
 
+YAML configuration files SHOULD be parsed using [v1.2 YAML core schema](https://yaml.org/spec/1.2.2/#103-core-schema).
+
 YAML configuration files MUST use file extensions `.yaml` or `.yml`.
 
 ### Environment variable substitution