feat: add option to use slug as title of post

[uiolee]

What does it do?

use slug as title of post when title is not specified.

closed #5372

Screenshots

Pull request tasks

• Add test cases for the changes.
• Passed the CI test.
• add to configuration

[github-actions]

Flamegraph

https://3fc8d4fd4e699700cba7676b67e3b62818aa9e1b-14-hexo.surge.sh/flamegraph.html
https://3fc8d4fd4e699700cba7676b67e3b62818aa9e1b-16-hexo.surge.sh/flamegraph.html
https://3fc8d4fd4e699700cba7676b67e3b62818aa9e1b-18-hexo.surge.sh/flamegraph.html

[coveralls]

Pull Request Test Coverage Report for Build 8773964452

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 10 of 10 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.001%) to 99.03%

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Totals
Change from base Build 8720332933:	0.001%
Covered Lines:	9293
Relevant Lines:	9384

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💛 - Coveralls

[stevenjoezhang]

See also #4344
Adding a new option is a good solution, especially if the theme does not support empty titles

[github-actions]

How to test

git clone -b filename https://github.com/hexojs/hexo.git
cd hexo
npm install
npm test