api: Split save action into separate API module

This allows us to make the token no longer a requirement
for non-save actions while still using the built-in system
for token verification.

Update documentation for "oldid" since it is not required even
outside (paction=save). In fact, if we require it VE loading
fails because it doesn't pass oldid unless it has to when
restoring a specific version.

Bug: 50424
Change-Id: I7b1b50a43648b1cc40a984340846efdb0ba2ecc9
Merge "api: Split save action into separate API module"