Increase the default priority class shares to 200 (on stable branches)

[mykaul]

Follow up of #13753 (comment)

[michoecho]

Note: doesn't apply to current master (after 66e4391), only to stable branches.

[bhalevy]

@michoecho can you please submit a PR for 5.3 fixing this issue and we'll backport it from there?

[michoecho]

@michoecho can you please submit a PR for 5.3 fixing this issue and we'll backport it from there?

It's a seastar-side change, so it will be fixed in Scylla when scylladb/seastar#1706 is applied to branch 5.3 in https://github.com/scylladb/scylla-seastar, and branch 5.3 in Scylla is updated to use that updated Seastar branch.

(And ditto for 5.2/5.1).