release-19.1: ui: adjust QPS Summary to match Time Series and Node Map values.

[celiala]

Backport 1/1 commits from #35693.

/cc @cockroachdb/release

---

In #283 and #23967,
we note three QPS-related areas in the Admin UI that were causing confusion
for users:

• The SQL Queries Metric, which shows QPS data for
  SELECT/INSERT/UPDATE/DELETE SQL queries.
• The Node Map, which shows QPS data for
  SELECT/INSERT/UPDATE/DELETE SQL queries.
• The 'Queries per second' in the Summary Bar, which calcuates QPS for all
  SQL queries (SELECT/INSERT/UPDATE/DELETE, but also includes DDL statements
  and transaction boundaries).

This commit:

• Updates the 'Queries per second' in the Summary Bar to just
  summarize the query types displayed in SQL Queries Time Series Metric and
  Node Map
• Clarifies which queries are included in Summary Bar with summary stat
  message.
• Removes P50 latency metric, since:
  • latency metrics still include all queries and this change might
    introduce new user questions/confusion.
  • our support team has confirmed that while users care about P99 and P90,
    we actually don't see customers concerned about P50.
  • [Why P50 but not P90] For the P90 & P99 metrics, a push up will most
    likely be from normal SELECT/INSERT/UPDATE/DELETEs. For 50, however,
    if clients are doing a large number of complex transactions or SET
    commands this could really skew the P50 result.

While this doesn't fully address all the concerns raised from #283 and #23967,
this at least provides a short-term fix of making all the numbers consistent.

Time Series vs Summary Bar. Before (discrepancy of 142.9):

Time Series vs Summary Bar. After (sums match up):

Node Map vs Summary Bar. After (sums match up):

Updated Summary Bar:

Release note (admin ui change): 'Queries per second' metric in Summary Bar
adjusted to only summarize the query types displayed in SQL Queries Time
Series Metric and Node Map.

[cockroach-teamcity]

This change is 

[knz]

this will get a green build when #35939 merges. it's green now

[celiala]

bors r+

[celiala]

just remembered:

we use the github green merge button instead of bors.

bors r-

[craig]

Canceled