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.

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

{
  "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.