docs: Add deprecation note, update /install page

[vikram-dagger]

This commit adds a new deprecation notice to all documentation pages under /0.1 and /0.2.

The content of the deprecation notice is stored as a partial.

Since #3908 is related, this commit also creates a new page at the mutable /install endpoint with links to the SDK installation pages. The previous /install page is relocated to a new URL /1242/install. Links are adjusted in older navigation bars.

Relates to #3904 . Closes #3908 .

Signed-off-by: Vikram Vaswani [email protected]