Check if configured tile size matches backend at startup

[pgporada]

At startup, check if the operator supplied tileSize value matches the backend and perhaps dynamically adjust the tileSize until enough entries exist to match the supplied value.

There's some edge cases of:

1. A brand new log with no entries
2. A log without enough entries for the first tile

https://github.com/jsha/ctile/blob/8dc3ca255f6a3a1a10b1386942d693d4abcbe825/main.go#L299

[pgporada]

I think the intent is for ctile to pass these requests through to the log instead of doing any caching.