Update Firebolt features and connection parameters

[ptiurin]

What are you changing in this pull request and why?

Firebolt has rolled out a new authentication method with service account credentials, all new Firebolt DBT users would use it from now on. Existing dbt-firebolt connector handles this behind the scenes allowing users that haven't migrated yet to use their old credentials while also allowing new customers to use the recommended way of authentication. This change in documentation reflects the new auth to avoid confusion for the new users.

Also updating some of the outdated information on Firebolt features supported, like removal of Join indexes and engine types and updating doc links to the new website.

Checklist

• Review the Content style guide so my content adheres to these guidelines.
• For docs versioning, review how to version a whole page and version a block of content.

Adding or removing pages (delete if not applicable):

• Run link testing locally with npm run build to update the links that point to deleted pages

[welcome]

Hello!👋 Thanks for contributing to the dbt product documentation and opening this pull request! ✨
We use Markdown and some HTML to write the dbt product documentation. When writing content, you can use our style guide and content types to understand our writing standards and how we organize information in the dbt product docs.
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Name	Status	Preview	Updated (UTC)
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[mirnawong1]

Suggested change

	## How Aggregating Indexes Are Named
	## How aggregating indexes are named

[mirnawong1]

thanks for opening this up @ptiurin , will get this merged for you!

[mirnawong1]

hey @ptiurin , thanks for opening this pr! I'm trying to update this branch but i don't have permissions. any chance you can update the branch on your end before i merge?

[ptiurin]

Hi @mirnawong1 , sorry I was OOO so didn't catch your comment in time. Thanks for merging this PR! Do you want me to create another with the changes proposed here?