Reorganize RPC+SDK related content in Guides section

[mollykarcher]

The How-To Guides section of the docs contains a grab-bag of different content. There is an "RPC" section but the content there is mostly focused on SDK-specific usage. There's some similar content under the "Transactions" subsection. Most of the guides in this section are full-stack lifecycle style guides, so RPC is often a piece of that puzzle but it seems strange to have a specific "RPC" section here. I'm not proposing a specific solution here but it requires brainstorming as to what we'd like to do with this content; whether we'd like to move it somewhere else, remove it, or keep it as is.