"
Start converting small functions in gossiper code
from using `seastar::thread` context to coroutines.
For now, the changes are quite trivial.
Later, larger code fragments will be converted
to eliminate uses of `seastar::async` function calls.
Moving the code to coroutines makes the code a bit
more readable and also mmediately evident that a given
function is async just looking at the signature (for
example, for void-returning functions, a coroutine
will return `future<>` instead of `void` in case of
a seastar::thread-using function).
Tests: unit(dev)
"
* 'coro_gossip_v1' of https://github.com/ManManson/scylla:
gms: gossiper: coroutinize `maybe_enable_features`
gms: gossiper: coroutinize `wait_alive`
gms: gossiper: coroutinize `add_saved_endpoint`
gms: gossiper: coroutinize `evict_from_membership`
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