Dev documentation: update title tag props comment or description to explain its usage

[daine]

📇 User story

As a developer I want to know what the notice-title-tag and card-title-tag properties actually do so that I can use them effectively

✅ Definition of Done / Outcomes

• Done when it is clear that the notice-title-tag and card-title-tag properties only set the title tag to a different heading level for semantic / accessibility purposes, so that it appears in the correct order in the accessibility tree. It does not change the visual appearance of the title tag itself.

📜 Acceptance criteria

• Comments in the stencil prop have been updated
• README on the components affected have been updated (this should be auto generated)
• The documentation website guidance on the code mentions this clearly
• Check if this behaviour exists for any other component or property apart from the Notice and Card components

[melaniebmn]

Component descriptions were done in this PR. Documentation site changes were done in this PR.

Currently blocked by translation for the new documentation site content.