Add last indexed block

[fmrsabino]

In order to provide better visibility on the indexing status of each chain, we should show the latest indexed block number for that chain.

@gnosis/safe-services

[fmrsabino]

Currently upptime allows to run custom javascript on the root status page (https://upptime.js.org/docs/configuration/#custom-javascript). However the root page contains not only entries for the core services but also for the client gateway.

A solution would be to:

1. Run custom javascript to fetch the blocks for all networks (need to keep a hardcoded list with the endpoints for all networks)
2. Update the entries (HTML) with the block number – accessing the specific div block might not be straightforward as the ids are generated.

This solution does not seem robust enough for us to maintain as upptime seems to have not be made to have custom fields backed by the payloads returned on the endpoints.

[Uxio0]

That seems a little overcomplicated. I opened #14

[rmeissner]

Close in favor of #14