chore: make parameterizible cache size

[Ivansete-status]

Background

The nwaku node has multiple caches and they have a default and hard-coded cache size.
We need to make the cache sizes configurable so that they can be easily changed.

Details

This issue was originally detected by @fbarbu15, who tried to use the /filter/v2/messages REST service from both nim-waku and go-waku , and found discrepancies between them.

The place where we have the max message size hard-coded:

nwaku/waku/waku_api/message_cache.nim

Line 18 in 07beea0

const DefaultMessageCacheCapacity: int = 50

Ideally, we need to have these two similar parameters in nwaku:
https://github.com/waku-org/go-waku/blob/master/cmd/waku/flags.go#L541-L553

Original Discord conversation:

Acceptance criteria

Have the same level of cache-size reconfigurability that we have in go-waku.

[SionoiS]

You can configure caches but not at the app level I guess?

nwaku/waku/waku_api/message_cache.nim

Line 38 in 07beea0

func init*(T: type MessageCache, capacity=DefaultMessageCacheCapacity): T =