Specify initial serialization buffer capacity for Payloads

Specify initial serialization buffer capacity for Payloads

JFR shows a lot of re-allocations of the backing byte [] when
serializing CommitTransactionPayload. Specify a reasonable
initial buffer capacity (the default in ByteArrayOutputStream
is 32) to reduce re-allocations. This is also configurable via
the cfg file (default is 512).

Also did the same for the other smaller Payload classes like
PurgeTransactionPayload.

JIRA: CONTROLLER-1870
Change-Id: I7ebced56812bfc102409b5b2a8b7f4b1b54359fc
Signed-off-by: Tom Pantelis <tompantelis@gmail.com>