Ability to configure semantic version for each commit type

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**Is your feature request related to a problem? Please describe.**
Users are able to configure the Release Please action to recognise additional commit types by adding them to the `changelog-sections` in the `release-please-config.json` file. However, any commit type other than `feat` and `fix` will result in a patch version and there is currently no way to change that (except by manually editing the manifest file on the release PR branch).

**Describe the solution you'd like**
I'd like to be able to configure the semantic version associated with each commit type somehow, rather than it always defaulting to a patch version. For example, I'd like to configure the `build` commit type to result in a minor version. This could be achieved via the `changelog-sections` in the `release-please-config.json`, for example:
```
{
"packages": {
".": {
"release-type": "simple",
"changelog-sections": [
{
"type": "build",
"section": "🧰 Maintenance",
"semantic-version": "minor"
}
]
}
}
}
```

**Describe alternatives you've considered**
A workaround is to manual editing the manifest file on the release PR branch, but these changes are overwritten the next time a PR is merged to main and the release PR is updated. It is less than ideal when commit types other than `feat` and `fix` are frequently used and the version has to be manually altered.

**Additional context**
Please see above.