Provide a link to the Grafana logs before the command starts executing

[joao-paulo-parity]

When we post a "Starting benchmark..." comment, it would be great to also include a link to the Grafana logs starting from where the command began executing (i.e. not here since it is not executing yet).

Instead of the current:

1. Post an initial comment
2. Update the comment once the benchmark finishes

Do the following:

1. Post an initial "acknowledgement" comment in response to the request
2. When the benchmark begins executing, update the comment with the log's links based on start time
3. When the command finishes, update the comment with the results

The start time for Grafana logs can be set through URL query parameters.

The message could be similar to what's done in try-runtime-bot but even better than that because we'll also be including a directly link to the logs, not only the query.