Update recording errors doc - document when to use error, exception (or both) attributes

[lmolkova]

Fixes #2001

Updates errors guidance to cover:

• errors vs exceptions and when to use which set of attributes
• reporting errors on logs/events
• reporting error.message attribute

[braydonk]

How does this mesh with languages that don't have "exceptions" and actually only have "errors" like Go or Rust?

[lmolkova]

I refactored it slightly, please take a look, the key change:

added

Errors and exceptions are related but not the same: an error can occur without
an exception being thrown, and an exception does not necessarily constitute an
error.

Exceptions and how they are recorded in telemetry are inherently
language-specific. Some languages, such as Rust or Go, do not use exceptions
at all.

This document focuses on recording errors.

Plus there are a couple of points below that should address it

• Semantic conventions intended for cross-language applicability SHOULD use
  error.* attributes.

• exception attributes SHOULD be documented for conventions that target
  exceptions directly such as exception events.