Update default validator selection for staking

[nampc1]

We should implement an algorithm to automatically select the best validators for user staking directly through nomination

• [x] Step 1: Implement logic
• [x] Step 2: Implement UI

[bluezdot]

Use activeEra instead of currentEra for fetching last-14-eras points. Because when currentEra jumps to a new era, activeEra is still in the previous era, and the era point is still distributed.

[Sokol142196]

@bluezdot please describe the Validator selection algorithm

[bluezdot]

@Sokol142196 The algorithm to select the top 50% validator is in the following step:

1. At the current era n, I fetch all validators's point information from era n-14 to era n-1 (14 eras in total).
2. Calculate the total point of each validator that appears with this format: validator_address: total_point.
3. Sort the list of validators by total_point in descending order.
4. Filter the top 50% from the list in step 3.

Above is the algorithm from background logic. The remaining algorithm to select 16 validators is implemented by @lw-cdm. 

[ThaoNguyen998]

Validation passed. Check with Polkadot: Top 50% validator

polkadot.txt

https://konistudio-my.sharepoint.com/:x:/g/personal/nhungphung_koni_studio/EXAYw6nH8MhFmunGwYWTpIcBn5B2_l_51nIwaalvxPAGLg?e=YtMmkz

[Sokol142196]

Needs discussion and improvement in case there is already a stake