sql: do not consider TCL stmts in sql stats tracing

[xinhaoz]

For SQL stats we trace every new fingerprint in an application
container in order to populate statistics that are only available
via tracing for each fingerprint. This sampling logic worked by
tracking the SQL fingerprint strings encountered by each application
but did not factor in fingerprints that are not tracked by SQL stats,
such as TCL statements (BEGIN, COMMIT, ROLLBACK), were being treated
as new fingerprints on each execution which resulted in tracing being
turned on. This commit ensures that we don't consider TCL statements
in this sampling strategy. TestSampledStatsCollectionOnNewFingerprint
is also fixed as it was assuming that previously seen statements in
new transactions would trigger this sampling behaviour when it should
not - this was being erronneously triggered by BEGIN.

name                                   old time/op    new time/op    delta
Sysbench/SQL/3node/oltp_read_write-10    5.61ms ± 3%    5.69ms ± 4%    ~     (p=0.167 n=8+9)

name                                   old alloc/op   new alloc/op   delta
Sysbench/SQL/3node/oltp_read_write-10    2.15MB ± 2%    2.12MB ± 2%  -1.24%  (p=0.029 n=10+10)

name                                   old allocs/op  new allocs/op  delta
Sysbench/SQL/3node/oltp_read_write-10     10.7k ± 1%     10.5k ± 0%  -1.69%  (p=0.000 n=10+9)

Epic: none
Part of: #133307

Release note: None

[blathers-crl]

It looks like your PR touches production code but doesn't add or edit any test code. Did you consider adding tests to your PR?

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[cockroach-teamcity]

This change is