allow setting first week epoch in farm

[dorin-iancu]

Added the possibility of setting first_week_start_epoch when deploying the farm contracts.

Also done some misc changes:

• reorder some conditions for early-exit
• removed set_if_empty. No longer needed since we have a separate method
• also removed the migration code from the init function

[github-actions]

Contract comparison - from cad0c11 to 2ed5386

Path	size	has-allocator	has-format
mx-exchange-sc
- pause-all/pause-all.wasm	5548	No	No
mx-exchange-sc/dex
- farm/farm.wasm	38759 ➡️ 38842 🔴	No	No
- farm-with-locked-rewards/farm-with-locked-rewards.wasm	38439 ➡️ 38525 🔴	No	No
- governance/governance.wasm	17355	No	No
- pair
- - pair.wasm	31271	No	No
- - pair-full.wasm	32650	No	No
- - safe-price-view.wasm	7888	No	No
- pair-mock/pair-mock.wasm	5470	No	No
- price-discovery/price-discovery.wasm	16381	No	No
- proxy-deployer/proxy-deployer.wasm	4502 ➡️ 4578 🔴	No	No
- router/router.wasm	26718	No	No
mx-exchange-sc/energy-integration
- energy-factory-mock/energy-factory-mock.wasm	4277	No	No
- energy-update/energy-update.wasm	1558	No	No
- fees-collector/fees-collector.wasm	18953	No	No
- governance-v2/governance-v2.wasm	16680	No	No
mx-exchange-sc/farm-staking
- farm-staking/farm-staking.wasm	43393 ➡️ 43517 🔴	No	No
- farm-staking-proxy/farm-staking-proxy.wasm	19393	No	No
- metabonding-staking/metabonding-staking.wasm	10176	No	No
mx-exchange-sc/locked-asset
- distribution/distribution.wasm	14292	No	No
- energy-factory/energy-factory.wasm	35029	No	No
- factory/factory.wasm	30471	No	No
- lkmex-transfer/lkmex-transfer.wasm	11288	No	No
- locked-token-wrapper/locked-token-wrapper.wasm	14586	No	No
- proxy_dex/proxy_dex.wasm	36917	No	No
- simple-lock/simple-lock.wasm	24491	No	No
- simple-lock-whitelist/simple-lock-whitelist.wasm	26210	No	No
- token-unstake/token-unstake.wasm	14288	No	No

[psorinionut]

Do we need the extra check in place? We already have the check when computing the actual rewards. Maybe we accept that until the first_week_start_epoch is reached, we don't fail the endpoint, and just return 0. Then, after we pass that particular epoch, we avoid the 2 extra reads.

[psorinionut]

I would add a check in the startProduceRewards endpoint, to not allow the rewards to start generating, if current_epoch < first_week_start_epoch. This way, we avoid getting to the point where we may call an endpoint (like enterFarm) that calls the take_reward_slice function, which then would throw a SC error.

The base branch was changed.