feat: Improve usability of manifest types

[zshipko]

• Adds some helper functions for creating a manifest, mostly helpful for the Rust SDK
• Renames ManifestWasm to Wasm
• Renames ManifestMemory to MemoryOptions
• ManifestWasm and ManifestMemory have been marked as deprecated
• Adds an alias from MemoryOptions::max_pages to MemoryOptions::max in serde specification

[nilslice]

nice - just dropping a note to remind us that we will also need to update:
https://extism.org/docs/concepts/manifest

and the graphic that @bhelx generated. ben, what did you use to make that?

[bhelx]

I believe it was this: https://jlblcc.github.io/json-schema-viewer/

There is probably a way to render it in the docs.

[bhelx]

Since we've committed to the API, can we do this in a backwards compatible way? or save it for 1.0?

[nilslice]

If we're going to make some changes like this, there's another I'd like to consider in the HttpRequest type: header -> headers

[zshipko]

This PR should be backward compatible, with the old names marked as deprecated

@nilslice - I will add headers as an alias for header right now

[zshipko]

I just realized the max/max_pages and header/headers changes weren't present in the json schema because they were only aliases so I swapped the name of the struct fields and the alias names.

[nilslice]

Added a commit to include similar name changes throughout the SDKs. Figure we should be consistent. This breaks backward-compatibility though, so we should discuss.

[nilslice]

LGTM if you're ok with it @zshipko