Display total block size for the block chain

Like BTC has for theirs at: https://blockchain.info/charts/blocks-size

we should have one at
https://explorer.lbry.io/charts/blocks-size

## Internal Use

### Acceptance Criteria
1.
2.
3.

### Definition of Done
- [ ] Tested against acceptance criteria
- [ ] Tested against the assumptions of the user story
- [ ] The project builds without errors
- [ ] Unit tests are written and passing
- [ ] Tests on devices/browsers listed in the issue have passed
- [ ] QA performed & issues resolved
- [ ] Refactoring completed
- [ ] Any configuration or build changes documented
- [ ] Documentation updated
- [ ] Peer Code Review performed

Start by reviewing the existing chart implementation in the block explorer and compare its data source and presentation with the referenced blockchain.info blocks-size chart. Define the expected total block-size calculation and chart behavior before making changes, then add or update tests and verify the project builds successfully.

Written by the indexing model from the issue text.