Increase transaction list size for /v1/txn endpoint

[adoyle51]

Because the /v1/txn endpoint has a limit of 64 transactions per request, transaction performance suffers when performing thousands of transactions at once. Much of the degredation appears to be due to waiting for HTTP responses from Consul when sending thousands of 64 operation transaction payloads.

I reached out to the mailing group with this message here, and it was stated that it would be possible to increase the txn transaction limit.

consul version for both Client and Server

Client: 0.8
Server: 0.8

Operating system and Environment details

CentOS7
AWS EC2 t2.large instances

Please let me know if there is any other information I should provide in this request.

[slackpad]

We should do #2652 at the same time.

[tkrisko]

I think the transaction size should be either unlimited or there should be a way
to bind subsequent transactions together so API client can commit or revoke them. Current approach with specified limit still forces API client to split operations into "smaller" chunks what requires the client has to implement own transactional approach.

[vaidik]

Did we make any progress on this? It looks like that the limit of 64 txns is still there and the only way to handle this is what @krzyszko has suggested

[danparisi]

I am also wondering if this feature will be implemented

[osher]

we need this too.
the idea of breaking a transaction that should be atomic to separate operations feels wrong...

[msiege2]

This issue has been implemented with #14599 and will be in the next major Consul release.