ref-manual: New section clarifying stamps, input checksums and sstate cache

ref-manual: New section clarifying stamps, input checksums and sstate cache

Fixes [YOCTO #10172]

I added a new section on how BitBake reruns tasks based on the
stamps files.  Also put in some cross-referencing links to that
new section in the stamps entry for the structure chapter and in
the STAMP variable in the glossary.

(From yocto-docs rev: da8779d9eb85473cd6b0f74e9e1371e1d277890f)

Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>