docs: add missing "How to" in page titles

[dwilding]

A tiny PR to add "How to" in the titles of a few how-to guides.

[Copilot]

Pull request overview

This PR standardizes the titles of how-to guide documentation pages by adding the "How to" prefix to four page titles, making them consistent with how-to guide naming conventions.

Changes:

• Updated page titles in four how-to guide files to include the "How to" prefix

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
docs/howto/manage-libraries.md	Added "How to" prefix to "Manage libraries" title
docs/howto/manage-leadership-changes.md	Added "How to" prefix to "Manage leadership changes" title
docs/howto/manage-configuration.md	Added "How to" prefix to "Manage configuration" title
docs/howto/make-your-charm-discoverable.md	Added "How to" prefix to "Make your charm discoverable" title

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[dimaqq]

I'm not sure about the proposed change.

Why change these four but the other two dozen?
Why change at all, when these are entries under the How-to section in the TOC?

[dwilding]

Most of our how-to pages follow this convention:

• Page title (displayed on the page itself) is "How to do the thing"
• What's displayed in the site navigation is "Do the thing", for a more efficient use of space

Arguably we could drop "How to" from all pages, yes. But the majority already follow the established pattern - in this PR I'm fixing up the four that don't.

[dwilding]

I should add: The title in each foo.md file isn't what controls what appears in the site navigation. The site navigation entries are defined separately in the index.md files under each category.