Add translation string for Play Youtube Video button aria-label

[audrasjb]

Description

See this issue on WP-Rocket: wp-media/wp-rocket#7202
And the following PR: wp-media/wp-rocket#7203

Type of change

• New feature (non-breaking change which adds functionality).
• Bug fix (non-breaking change which fixes an issue).
• Enhancement (non-breaking change which improves an existing functionality).
• Breaking change (fix or feature that would cause existing functionality to not work as before).
• Sub-task of #(issue number)
• Chore
• Release

Detailed scenario

See wp-media/wp-rocket#7203

Technical description

See wp-media/wp-rocket#7203

Documentation

See wp-media/wp-rocket#7203

New dependencies

None

Risks

None

Mandatory Checklist

Code validation

• I validated all the Acceptance Criteria. If possible, provide screenshots or videos.
• I triggered all changed lines of code at least once without new errors/warnings/notices.
• I implemented built-in tests to cover the new/changed code.

Code style

• I wrote a self-explanatory code about what it does.
• I protected entry points against unexpected inputs.
• I did not introduce unnecessary complexity.
• Output messages (errors, notices, logs) are explicit enough for users to understand the issue and are actionnable.

Additional Checks

• In the case of complex code, I wrote comments to explain it.
• When possible, I prepared ways to observe the implemented system (logs, data, etc.).
• I added error handling logic when using functions that could throw errors (HTTP/API request, filesystem, etc.)

[audrasjb]

My only concern is the gettext string text-domain.
I used the slug of this library as text-domain but this implies that any project using this library will have to change the related text-domain accordingly. I didn't find any other user facing string in this library.

Another option would be to replace the gettext translation string with a filter that could be used by other projects to replace the string with a gettext translation string.

What do you think?