feat: make <TableHead> slot more flexible

[RyanZhiNie]

📑 Description

The current <TableHead> component just put the slot in a <tr> element. This weakens the flexibility of this component, such as multiple head rows or style modification on head rows. For the sake of compatibility with users' existing code, I add a boolean prop defaultRow rather than deleting that single <tr> element.

✅ Checks

• My pull request adheres to the code style of this project
• My code requires changes to the documentation
• I have updated the documentation as required
• I have checked the page with https://validator.unl.edu/
• All the tests have passed
• My pull request is based on the latest commit (not the npm version).

[vercel]

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Name	Status	Preview	Comments	Updated
flowbite-svelte	✅ Ready (Inspect)	Visit Preview	💬 Add your feedback	Jan 14, 2023 at 6:41AM (UTC)
flowbite-svelte-update	✅ Ready (Inspect)	Visit Preview	💬 Add your feedback	Jan 14, 2023 at 6:41AM (UTC)

[shinokada]

Thank you for your PR.
Can you run tests by npm run test?
Can you also confirm this is based on the latest commit.
Once they are done, please check in the boxes.

[RyanZhiNie]

I have updated my PR to let it be based on the latest commit, but unluckily I cannot successfully start up the tests with trying 10 times, it kept timeout. However, my local dev and the two previews deployed by the github vercel bot all don't show any bug, so this PR may be safe enough to be merged. It's okay to let this PR wait for a few days, I will try to run the tests more times.

[RyanZhiNie]

After adjusting the playwright webServer.timeout configuration to 300000, I finally started up the tests, and except xxx page should have h1, there were no other failed tests. BTW, this PR is updated again to be based on the latest commit.