Rewrite in-app documentation

[PE39806]

• Remove all legacy frontend/pages/docs/v1 docs
• Add new docs
• Add new style guide page
• Rewrite some existing docs to improve consistency and detail
• Improve styling of docs sidebar title text size to differentiate nested levels more clearly
• Improve documentation best practices for RAG applications

[ARADDCC002]

This is going to be a massive change... but should consider changing the capitalisation of the various headings and sub-headings?

For example, a sub-head of ## Example Sub-Heading, would become ## Example sub-heading. This wouldn't apply to proper nouns or anagrams, of course.

As this PR is already massive I'm happy for this to be done in the future.

[JRB66955]

Read through the documentation (in-app) sequentially up to the Inferencing tab, happy about it other than my sole comment so far.

[PE39806]

This is going to be a massive change... but should consider changing the capitalisation of the various headings and sub-headings?

For example, a sub-head of ## Example Sub-Heading, would become ## Example sub-heading. This wouldn't apply to proper nouns or anagrams, of course.

As this PR is already massive I'm happy for this to be done in the future.

Just to make sure I've understood this correctly, the highest level (h1 equivalent #) should be Title Case and all subheadings (h2 equivalent ## etc.) should be Sentence case?

[IR96334]

LGTM

[GB907762]

I think I've got through it all now😆

LGTM