Change url.query requirement level from recommended to conditionally_required (to match url.path)

[trask]

Spinning this out from #109 as a separate issue.

Summarizing the discussion:

Pro: this seems like a bug that slipped into open-telemetry/opentelemetry-specification#3355
Con: query is particularly prone to containing sensitive information

[trask]

from @Oberon00's #109 (comment)

it seems OK to be "just" recommended. I think that would allow instrumentations to provide an opt-out option which REQUIRED technically doesn't.

this is an interesting point

[lmolkova]

when sanitizing sensitive information, would we rather redact the values (i.e. foo=REDACTED&bar=REDACTED) or drop the attribute completely?

My preference is to preserve parameter names, order, etc rather than dropping the whole attribute.

I assume if users write sanitization, they do it as a processor (now) and will take the query attribute, parse, and sanitize individual properties. If we provide a tracing configuration to sanitize arbitrary values, we'd do something similar.

TLDR:

Opting-out needs configuration and this configuration would rather be a regex or a callback to sanitize than a boolean flag (drop/preserve).

Also, I feel we don't need to solve this problem prior to stability: it should not be breaking to switch between recommended and conditionally_required: when available at any moment.