Add common image attributes

[zadeviggers]

Summary

Summarize the changes briefly, including which issue/ticket this resolves. If it closes an existing Github issue, include "Closes #[issue number]"

Allow common image attributes by default. If the src attribute is going to be enabled without images being enabled, it makes sense to also allow other commonly used tags to reduce confusion when using the library.

The alt attribute is also required on <img /> tags by the HTML standard so it shouldn't be removed by default.

Closes #525

What kind of change does this PR introduce?

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• Bug fix
• New feature
• Refactor
• Documentation
• Build-related changes
• Other

Make sure the PR fulfills these requirements:

• It includes a) the existing issue ID being resolved, b) a convincing reason for adding this feature, or c) a clear description of the bug it resolves
• The changelog is updated
• Related documentation has been updated
• Related tests have been updated

If adding a new feature without an already open issue, it's best to open a feature request issue first and wait for approval before working on it.

Other information:

[boutell]

Thanks!