Clarify guidance regarding excessive logging

[alanwest]

Fixes #3147

Clarifies guidance with regards to logging when items (attributes, span links/events) are dropped or truncated on spans or log records.

I'm not certain what was originally intended to be communicated, so my initial proposal is to state that a message must only be printed once per Span/LogRecord regardless of how many items were dropped or truncated on the Span/LogRecord. However, some may argue this too may lead to excessive logging.

So the real question is what do we want to communicate here?

Another option may be to state something like:

To prevent excessive logging, an SDK SHOULD take measures to limit how often it notifies the user an attribute was discarded or truncated. The exact measures an SDK takes is not specified.

[carlosalberto]

Let's mention this in the maintainers meeting next Monday, so this is not a surprise, etc.

[tigrannajaryan]

Let's mention this in the maintainers meeting next Monday, so this is not a surprise, etc.

Good point. I think this also requires a changelog entry.