Add pre and post instrument entrypoints

[ocelotl]

Fixes #1982

[aabmass]

I think @owais made a good point in the SIG. Should we make this PR additive of the new entry points only and put a comment that opentelemetry_distro entrypoint is deprecated?

Could you also add some documentation on the opentelemetry-{pre,post}-instrument entry points since this is general purpose and anyone can use it. Maybe some of the figures from the slides you presented too?

[ocelotl]

I think @owais made a good point in the SIG. Should we make this PR additive of the new entry points only and put a comment that opentelemetry_distro entrypoint is deprecated?

I don't intend to deprecate opentelemetry_distro (I have renamed opentelemetry_distro to opentelemetry_configurator in #1966 because I found the latter name more representative than the first one, but it can be kept as opentelemetry_distro if the community prefers).

[owais]

@ocelotl I'm totally onboard with this PR. I was only suggesting we make this change gradually by keeping the distro hook as is for now and only adding pre/post hooks as new hooks. Once the configurator package you are working on that will provide distro hooks is ready and published, we can remove the distro hook from this package. It's still the same design as you presented but will be done in may be one additional PR.

[ocelotl]

Refactored this PR to only include the entry points

[owais]

We need changelog for this.

[ocelotl]

We need changelog for this.

added it 👍