Deprecate and reduce instrumenter usage internally

[sl0thentr0py]

Unclear currently how this is going to work in a backwards compat way

[szokeasaurusrex]

@sl0thentr0py, I think it is okay for us to drop instrumenter without deprecating it first and without making the change backwards compatible, since we already document instrumenter as being "for internal use only."

Ideally, we would remove the instrumenter in the Phase 1 major release; however, I would argue that since instrumenter is explicitly mentioned as being for internal use, we can safely remove it even in a minor version.

[sl0thentr0py]

We cannot remove the top level option though if someone is setting it in their init since that's breaking. We can remove all internal references but the init options has to be deprecated and stay till the major.
That being said, we will probably do a major anyway so let's see.

[szokeasaurusrex]

Fair enough @sl0thentr0py. Although, I would imagine that few, if any, users set a custom instrumenter in their init, since we don't seem to document this functionality anywhere, as far as I can tell (e.g., instrumenter is missing from this page).

Worst case, I think we can get away with emitting a DeprecationWarning when instrumenter is set and otherwise ignoring the parameter's value (perhaps technically breaking, but it at least won't break people's apps).

[sl0thentr0py]

it is required while using our span processor so far and is documented here
https://docs.sentry.io/platforms/python/tracing/instrumentation/opentelemetry/#usage

side note: while searching for docs usages, it is better as a dev to grep for a keyword in the docs repo rather than looking through the website to find something

[szokeasaurusrex]

Okay @sl0thentr0py, thanks for the link and the tip on docs searching.

I think in that case, let's just keep the instrumenter option in the top-level API and emit a deprecation warning when the user passes the instrumenter parameter.

[szokeasaurusrex]

We have decided to split this task as follows:

• Clarifying that instrumenter parameters (except to init) are internal-only (docs: Clarify that instrumenter is internal-only #3299)
• Fully deprecating instrumenter option (feat: Deprecate instrumenter option #3308), to be merged in last 2.x version (tracking issue #3320)
• Removing the instrumenter option in the POTel base branch (Remove instrumenter in potel-base branch #3321)

[szokeasaurusrex]

Closing in favor of #3320 and #3321.