…9856)

Motivation:

Currently traces in botocore derive their service name from the service
and endpoint, ex. `aws.s3` or `aws.sqs`, and there is no way to change
the service name. Other integrations allow for changing the default
service name either by setting environment variables, or configuring
with `config['service']` or `config['service_name']`. This PR adds
support for these methods of overriding the service name, which allows
individual traces to have custom service names.

Examples:

```
@mock_s3
ddtrace.config.botocore['service_name'] = "botocore" # this sets service name to botocore.s3
ddtrace.config.botocore['service'] = "boto-service" # this overrides previous and sets service name to boto-service.s3
```

`export DD_BOTOCORE_SERVICE="boto" # this overrides previous settings
and sets service & service name to boto.s3
`
## Checklist
- [x] PR author has checked that all the criteria below are met
- The PR description includes an overview of the change
- The PR description articulates the motivation for the change
- The change includes tests OR the PR description describes a testing
strategy
- The PR description notes risks associated with the change, if any
- Newly-added code is easy to change
- The change follows the [library release note
guidelines](https://ddtrace.readthedocs.io/en/stable/releasenotes.html)
- The change includes or references documentation updates if necessary
- Backport labels are set (if
[applicable](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting))

## Reviewer Checklist
- [x] Reviewer has checked that all the criteria below are met
- Title is accurate
- All changes are related to the pull request's stated goal
- Avoids breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes
- Testing strategy adequately addresses listed risks
- Newly-added code is easy to change
- Release note makes sense to a user of the library
- If necessary, author has acknowledged and discussed the performance
implications of this PR as reported in the benchmarks PR comment
- Backport labels are set in a manner that is consistent with the
[release branch maintenance
policy](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting)

---------

Co-authored-by: Zachary Groves <[email protected]>
Co-authored-by: erikayasuda <[email protected]>
(cherry picked from commit 2bb0c4b)