Add note on Copilot sign out/in to troubleshooting page

[juliasilge]

Addresses posit-dev/positron#11330 with some more guidance on the Assistant troubleshooting page.

We'd probably want to keep this around for about a month or two.

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[juliasilge]

Do we like a little callout box for this?

https://deploy-preview-255--positron-posit-co.netlify.app/assistant-troubleshooting.html

[sharon-wang]

I like the visibility of the callout! I wonder if we should add it also/instead to:

positron-website/assistant-getting-started.qmd

Lines 83 to 110 in 48ad923

	## GitHub Copilot
	::: {.callout-important}
	Positron Assistant requires a **GitHub account with Copilot enabled**.
	<details>
	<summary>How to get GitHub Copilot access</summary>
	GitHub Copilot is a proprietary tool from GitHub. If you want to use GitHub Copilot, you need a [subscription for GitHub Copilot](https://docs.github.com/en/billing/managing-billing-for-github-copilot/about-billing-for-github-copilot) in your personal GitHub account or to be assigned a seat by an organization with a subscription for GitHub Copilot for Business.
	Students and faculty can use GitHub Copilot for free as part of the GitHub Education program. For more information, see the [GitHub Education page](https://education.github.com/).
	</details>
	:::
	### Add GitHub Copilot as a language model provider
	1. Run the command _Positron Assistant: Configure Language Model Providers_
	1. Select **GitHub Copilot** as the model provider.
	{width=600}
	1. Click the **Sign in** button to initiate GitHub's OAuth authentication flow.
	- Complete the authentication flow in your browser, and return to Positron when finished.
	::: {.callout-tip}
	If you are using Positron with a [remote SSH](remote-ssh.qmd) session, you will need to authenticate to GitHub on the _remote server_ as well. Follow [along on GitHub](https://github.com/posit-dev/positron/issues/8409) as we make improvements in this area.
	:::

Or for now, maybe removing the following callout as it contradicts the callout being added in this PR?

positron-website/assistant-getting-started.qmd

Lines 108 to 110 in 48ad923

	::: {.callout-tip}
	If you are using Positron with a [remote SSH](remote-ssh.qmd) session, you will need to authenticate to GitHub on the _remote server_ as well. Follow [along on GitHub](https://github.com/posit-dev/positron/issues/8409) as we make improvements in this area.
	:::

I'll take a closer look at the GitHub Copilot getting started docs as part of posit-dev/positron#11233.

[juliasilge]

I think I would lean against putting the callout on the "getting started" page since this doesn't apply to anybody new today.