dbapi2 fails to extract table name when using square brackets

[anderssonjohan]

Describe the bug: ...

Queries made to tables which requires escaping end up with the wrong span name.

The following spans are SELECTs from four different tables, but only two unique span names appear.

To Reproduce

Import package and call extract_signature:

>>> from elasticapm.instrumentation.packages import dbapi2
>>> dbapi2.extract_signature("SELECT username FROM user")
'SELECT FROM user'
>>> dbapi2.extract_signature("SELECT username FROM [user]")
'SELECT FROM ['

Environment (please complete the following information)

• OS: [e.g. Linux]
• Python version:
• Framework and version [e.g. Django 2.1]:
• APM Server version:
• Agent version:

Additional context

Add any other context about the problem here.

• Agent config options

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• requirements.txt:

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[aless10]

Hi, I would like to contribute and give it a try to fix this

[anderssonjohan]

@aless10 I'm touching the same thing in this PR. Perhaps you will find my parameterized test useful as boiler-plate code here: https://github.com/elastic/apm-agent-python/pull/1938/files