Deprecating APIs with microversions is a long-established pattern
at this point, but the docs don't mention it at all, so this
adds a short description of what happens there.
We removed the os-certificates and os-cloudpipe APIs in Pike
and the os-fping API in Rocky, and there is a pattern to removal
also, so this adds detailed documentation on the steps involved
in removing a deprecated API.
Change-Id: I9fdb9ce78c45d27d3c7f55fcbda0f763dfb66d66
d5202b5561