tf-a-lts-docs-watcher.sh: Convert Git tag to ReadTheDocs slug

There's not really one-to-one mapping between git tag and corresponding
RTD version slug, as soon as we get to more complex tags. For example,
tag "sandbox/lts-v2.10.3-20240229T100000" gets mapped by RTD to slug
"sandbox-lts-v2.10.3-20240229t100000". So, perform the mapping on our
side to get feed proper data to the RTD API.

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: If785cd31f25d6b2835c8b8b761ffad817765bf4b
1 file changed