Add "Total Count" to Indexer Search Transactions Response

[stuartwk]

Usually for paginated responses, a "total count" is available. Since there are offset and limit params, adding total_count to SearchTransactionsResponse would be helpful, especially when querying for address transactions.

[patrick-ogrady]

This makes sense to me, @stuartkuentzel! I've created an internal ticket and will include this in the next release.