mimir-continuous-test: add a flag not to search for series prior to the process start date

[ldvc]

Is your feature request related to a problem? Please describe.

When modifying deployment parameters (e.g. changing numSeries from 1000 to 10000), assertions on query results may fail during the MaxQueryAge timeframe as series have changed.

This can lead to invalid alerts, as they are linked to a change in the monitoring tool's configuration and not to a genuine failure of the infrastructure under test.

Describe the solution you'd like

We should offer a configuration flag to allow adjustedQueryMinTime not to be set before Mimir continuous-test current start time.

For example:

limit-max-query-age-by-startup-time true

Describe alternatives you've considered

None.

Additional context

I open this issue for discussion. If the outcome is positive, I could take care of the PR.