router pair map migration

[psorinionut]

• Added a new pair mapper that has the pair_address as a key.
• Includes a migration endpoint.

[github-actions]

Contract comparison - from 8405234 to 8300c57

Path	size	has-allocator	has-format
mx-exchange-sc
- pause-all/pause-all.wasm	5438	No	No
mx-exchange-sc/dex
- farm/farm.wasm	38165	No	No
- farm-with-locked-rewards/farm-with-locked-rewards.wasm	37846	No	No
- governance/governance.wasm	17283	No	No
- pair
- - pair.wasm	30521	No	No
- - pair-full.wasm	31968	No	No
- - safe-price-view.wasm	7862	No	No
- pair-mock/pair-mock.wasm	5474	No	No
- price-discovery/price-discovery.wasm	16254	No	No
- proxy-deployer/proxy-deployer.wasm	4457	No	No
- router/router.wasm	25299 ➡️ 25991 🔴	No	No
mx-exchange-sc/energy-integration
- energy-factory-mock/energy-factory-mock.wasm	4233	No	No
- energy-update/energy-update.wasm	1510	No	No
- fees-collector/fees-collector.wasm	18320	No	No
- governance-v2/governance-v2.wasm	16822	No	No
mx-exchange-sc/farm-staking
- farm-staking/farm-staking.wasm	41505	No	No
- farm-staking-proxy/farm-staking-proxy.wasm	22835	No	No
- metabonding-staking/metabonding-staking.wasm	9595	No	No
mx-exchange-sc/locked-asset
- distribution/distribution.wasm	14358	No	No
- energy-factory/energy-factory.wasm	34193	No	No
- factory/factory.wasm	30374	No	No
- lkmex-transfer/lkmex-transfer.wasm	11214	No	No
- locked-token-wrapper/locked-token-wrapper.wasm	14291	No	No
- proxy_dex/proxy_dex.wasm	34335	No	No
- simple-lock/simple-lock.wasm	24299	No	No
- simple-lock-whitelist/simple-lock-whitelist.wasm	25946	No	No
- token-unstake/token-unstake.wasm	13625	No	No