feat(cketh/ckerc20): consolidate log scrapings

[gregorydemay]

Follow-up on #2324 and #2369 to consolidate log scrapings done by the ckETH minter.

Added

Information related to the state of the scraping of the new deposit with subaccount helper smart contract:

1. Last scraped block number to MinterInfo.
2. State of scraping (address and last scraped block number) to the minter dashboard.
3. Metric for the last scraped block number.

Changed

Refactor State to have a container (LogScrapings) to aggregate all log scrapings. This allows to:

1. Automatically display the state of a new log scraping to the minter dashboard. Information related to helper smart contracts was moved to its own section.
2. Automatically add a metric for the last scraped block number.
3. Recall to add an event that is registered during pre-upgrade to save the last scraped block number to stable memory.

[ninegua]

Thanks! LGTM!

nit: there is a typo in your PR title, s/cker20/ckerc20/

[gregorydemay]

Thanks @ninegua for the review!

nit: there is a typo in your PR title, s/cker20/ckerc20/

Good catch!