Allow to overwrite `whatBump` function from presets

Hi, currently we are able to overwrite parserOpts and writerOpts:

https://github.com/semantic-release/release-notes-generator/blob/354354b1dabf404bebd637ab7850f3d0402aa325/lib/load-changelog-config.js#L35-L39

but we miss a capability to overwrite whatBump() function used by presets, e.g. conventional-changelog-conventionalcommits:

export default async function createPreset (config) {
  return {
    commits: {
      ignore: config?.ignoreCommits,
      merges: false
    },
    parser: createParserOpts(config),
    writer: await createWriterOpts(config),
    whatBump: createWhatBump(config)
  }
}

In case of this specific preset, whatBump() impacts the generated release notes because of a) commit object modification (which is a preset issue itself) b) hardcoded breakingHeaderPattern here:

export const breakingHeaderPattern = /^(\w*)(?:\((.*)\))?!: (.*)$/

which ignores the breakingHeaderPattern value passed to parserOpts (which, I guess, makes sense as whatBump() is a separate function). If we could overwrite a function - we would be able to align parser and whatBump() logic on our end.

Begin with lib/load-changelog-config.js at the linked parserOpts and writerOpts handling, then trace how presets supply whatBump, especially in conventional-changelog-conventionalcommits. Confirm that a caller can replace that function and that generated release notes use the replacement, including the breaking-header case.