Support configuring non-GitHub issue trackers

`conventional-changelog-conventionalcommits` provides the option to set `issuePrefixes` and `issueUrlFormat` to detect references to issues from non-GitHub issue trackers (e.g. Jira) and link to them in the changelog.

```js
const presetFactory = require('conventional-changelog-conventionalcommits');
presetFactory({
"issuePrefixes": ["TEST-"],
"issueUrlFormat": "myBugTracker.com/{prefix}{id}"
});
```

Right now release-please only allows to pass custom `types` to `conventional-changelog-conventionalcommits` by configuring `changelog-sections`:

https://github.com/googleapis/release-please/blob/422df5a6a9d44a52c6c682563d1795b8fd246215/src/changelog-notes/default.ts#L65-L69

Allowing us to configure something like
```json
{
"changelog-issue-prefixes": ["TEST-"],
"changelog-issue-url-format": "myBugTracker.com/{prefix}{id}"
}
```
and passing it to `conventional-changelog-conventionalcommits` would allow us to link to non-GitHub issues in the changelog created by release-please.