If no fresh data/update, show warning on website

[metachris]

If relayscan-website can't update it's data (i.e. lost connection to DB), it should show a warning on the website after some time

See also

• https://github.com/flashbots/relayscan/blob/main/services/website/webserver.go#L191
• https://github.com/flashbots/relayscan/blob/main/services/website/webserver.go#L150

Error was:

May 18 12:40:08 ip-172-31-22-191 relayscan[805455]: time="2023-05-18T12:40:08Z" level=info msg="updating 7d stats..."
stats for 24h" error="dial tcp DB_IP:5432: connect: connection timed out"

Improvement: instead of just logging the error, if the last generated data is >30min old, show a warning that there may be a problem and the data was last update "XXX time ago"

[metachris]

Ideally also warn if the last slot in the database is more than 30 min old

[metachris]

Related work was done in #44 (show time since last update)

[metachris]

Done with the "time since last update"