Inserts and updates to replicated capped collections must be single threaded

Similar to SERVER-21483, which limited concurrency on secondaries for capped collections, the same needs to happen on the primary. This will prevent the primary from running with more concurrency than the secondary.

Additionally we need to do this with inserts for correctness to ensure that the order of the capped collection matches the order of the insert entrees in the oplog.

Original title and description:
sys-perf regression: secondary could not keep with with insert_capped with WT (core_workloads_WT)

with insert_capped test, secondary cannot keep up with primary. This is introduced somewhere between c76b4ff to 0730c65,

• manually verified this issue.
• same workload insert into non-capped col does not show this issue.
• this happens with vector insert with 8+ threads
• primary and secondary show big difference in insert rate 150k vs 28k.
• the growth of replication lag is almost linear vs time.