Use new -mount syntax for all KV subcommands in 1.11 docs

[digivava]

I have updated all docs pages dealing with the KV CLI to use the new -mount flag syntax, which was created to mitigate confusion caused by the previous syntax for interacting with KV secrets in the CLI.

These docs pages will now match the text produced by calling a vault kv subcommand with the -help flag.

Background

This syntax is optional, allowing users to do vault kv get -mount=secret foo instead of the old vault kv get secret/foo. While the old way may look prettier, it turned out this syntax caused a lot of confusion for new users, who quickly run into issues caused by the fact that secret/foo looks like a path but is not actually the real path to the secret for KV v2 (secret/data/foo). The real path is used by policies and the API, so users fresh off the Getting Started guide often don't understand why their policies or CLI commands don't work when they try to use the same "path" for both.

Caveats

I continued to use the old syntax on the index page for CLI commands in general, since that page is aimed at showcasing concepts that are true across all Vault CLI commands. This mount flag syntax only works for the kv subcommands, so I didn't want to muddy the message of that page. So, on that page I call out the existence of this flag in a KV-specific paragraph down below, but otherwise leave those examples alone.

[taoism4504]

minor nits, but otherwise LGTM