Add filter replace_title to adjust entry titles

[M-Ahall]

Do you follow the guidelines?

• I have tested my changes
• I read this document: https://miniflux.app/faq.html#pull-request

I'm adding a lot of feeds from github releases, for example https://github.com/jesseduffield/lazygit/releases.atom. Titles are only v0.40.2, and I have to read the small description underneath the title to see which software has a new release.

Having an ability to replace in title as well as content would solve this nicely for me, replace_title("^"|"miniflux ").

[fguillot]

Is it possible to add at least one test case for this feature?

[M-Ahall]

Of course, one simple test coming right up!

[M-Ahall]

(replace_title perhaps should be replace_in_title or something else entirely? The functionality would be much more helpful to me than a specific name 😃)

[fguillot]

(replace_title perhaps should be replace_in_title or something else entirely? The functionality would be much more helpful to me than a specific name 😃)

replace_title looks good enough to me?