Update welcome message in docs

[rpeden]

This pull request updates the sample output on several docs pages to match the updated Prefect CLI output.

Follows up on changes made in #8434.

Example

Before:

 ___ ___ ___ ___ ___ ___ _____    ___  ___ ___ ___  _  _
| _ \ _ \ __| __| __/ __|_   _|  / _ \| _ \_ _/ _ \| \| |
|  _/   / _|| _|| _| (__  | |   | (_) |   /| | (_) | .` |
|_| |_|_\___|_| |___\___| |_|    \___/|_|_\___\___/|_|\_|

After:

 ___ ___ ___ ___ ___ ___ _____ 
| _ \ _ \ __| __| __/ __|_   _|
|  _/   / _|| _|| _| (__  | |
|_| |_|_\___|_| |___\___| |_|

This matches the new output of prefect server start:

prefect/src/prefect/cli/server.py

Lines 73 to 76 in f1cf110

	___ ___ ___ ___ ___ ___ _____
	| _ \ _ \ __| __| __/ __|_ _|
	| _/ / _|| _|| _| (__ | |
	|_| |_|_\___|_| |___\___| |_|

Checklist

• This pull request references any related issue by including "closes <link to issue>"
  • If no issue exists and your change is not a small fix, please create an issue first.
  • I believe this fix is too small to require an issue.
• This pull request includes tests or only affects documentation.
• This pull request includes a label categorizing the change e.g. fix, feature, enhancement

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