Add a chart for history of knowledge size

[Keith-CY]

Is your feature request related to a problem? Please describe.

The knowledge size is the size occupied by on-chain data, not the declared size of cells. It reveals how many resources are used to share common knowledge, which is an important index for users.

Describe the solution you'd like
The current knowledge size can be calculated as described in https://talk.nervos.org/t/how-to-get-the-average-occupied-bytes-per-live-cell-in-ckb/7138/2?u=keith

And here is the code

const EXCLUDE = BigNumber('504000000000000000')
const getKnowledgeSize = async (nodeUrl: string) => {
  const header = await fetch(nodeUrl, {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({
      id: 1,
      jsonrpc: '2.0',
      method: 'get_tip_header',
      params: [],
    }),
  })
    .then(res => res.json())
    .then(res => res.result)
  const { dao } = header

  const [, , , u] = dao
    .slice(2)
    .match(/\w{16}/g)
    .map((i: string) => i.match(/\w{2}/g)?.reverse().join('') ?? '')
  const total = BigNumber(`0x${u}`).minus(EXCLUDE).toFormat()
  return total
}

A chart of its history can be added in the explorer so we can see how it grew in the past.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

[rabbitz]

PR: nervosnetwork/ckb-explorer@de6f7d4

curl 'https://ckb-explorer-api-staging.magickbase.com/api/v1/daily_statistics/knowledge_size' \
  -H 'accept: application/vnd.api+json' \
  -H 'accept-language: zh-CN,zh;q=0.9,en;q=0.8,sa;q=0.7' \
  -H 'cache-control: no-cache' \
  -H 'content-type: application/vnd.api+json' 

[FrederLu]

Screenshot 1336491 This data is obtained through the dao of this block on 2020/05/23 00:00:42.
If you want to display the knowledge_size on May 23, it is best to use the dao data of this block on 2020/05/23 23:59:38.
Please confirm. @rabbitz

[FrederLu]

Verified.