feat(blog): add blog pageBasePath plugin option

[ilg-ul]

Pre-flight checklist

• I have read the Contributing Guidelines on pull requests.
• If this is a code change: I have written unit tests and/or added dogfooding pages to fully verify the new behavior.
• If this is a new API or substantial change: the PR has an accompanying issue (closes #0000) and the maintainers have approved on my working plan.

Motivation

In Docusaurus, the URL parts used to compose the paths are configurable via options like routeBasePath, tagsBasePath, etc, but in the path used for multi-page lists, a part of the URL is hard-coded as page.

Test Plan

TBD

Test links

TBD

Related issues/PRs

fix #9828

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[ilg-ul]

I did not find a way to test xxxBasePath definitions, to inspire from. :-(

Please advise on how to proceed.

[slorber]

LGTM, although tests are failing and should be updated.

You can test your feature in this existing test suite.

Note that it would be nice to also ensure that the code is not sensitive to the presence/absence of a path leading/trailing slash here

describe('paginateBlogPosts', () => {
  it('generates right pages', () => {
    const blogPosts = [
      {id: 'post1', metadata: {}, content: 'Foo 1'},
      {id: 'post2', metadata: {}, content: 'Foo 2'},
      {id: 'post3', metadata: {}, content: 'Foo 3'},
      {id: 'post4', metadata: {}, content: 'Foo 4'},
      {id: 'post5', metadata: {}, content: 'Foo 5'},
    ] as BlogPost[];
    expect(
      paginateBlogPosts({
        blogPosts,
        basePageUrl: '/blog',
        blogTitle: 'Blog Title',
        blogDescription: 'Blog Description',
        postsPerPageOption: 2,
      }),
    ).toMatchSnapshot();
    expect(
      paginateBlogPosts({
        blogPosts,
        basePageUrl: '/',
        blogTitle: 'Blog Title',
        blogDescription: 'Blog Description',
        postsPerPageOption: 2,
      }),
    ).toMatchSnapshot();
    expect(
      paginateBlogPosts({
        blogPosts,
        basePageUrl: '/',
        blogTitle: 'Blog Title',
        blogDescription: 'Blog Description',
        postsPerPageOption: 10,
      }),
    ).toMatchSnapshot();
  });
});

It currently fails because you didn't add the extra method param to that test suite.

---

Not relate to this PR but I noticed a useless param returned in the loaded content, I'd appreciate if you could remove it: blogTagsPaginated: []:
https://github.com/cronica-it/docusaurus-fork/blob/issue-9828/packages/docusaurus-plugin-content-blog/src/index.ts#L125

[ilg-ul]

I guess I addressed all requested changes and the tests passed.

[slorber]

LGTM 👍 I would add an extra test to paginateBlogPosts to actually cover this new feature

[slorber]

Thanks 👍 LGTM

[ilg-ul]

Thank you, Sébastien!