Change text/tooltip for Estimated Message/Record counts

[jason-da-redpanda]

The message count displayed in Console ..

We already have a message saying that the calculation(HighWaterMark-LogStartOffset) for topics defined as cleanup.policy=compact*....
as gaps in offsets can occur when compaction occurs.

but in the scenario of topics defined as 'cleanup.policy=delete` (or compact) .. there can also be apparent gaps ...
when using transactions to produce events. This is down to internal control records..which are not consumed by standard clients....

Which means the count is an estimate regardless of the cleanup.policy

Suggestion is

• change wording to say "Estimate Message Count" (or varation)
• Have a tooltip to detail reasons for deltas