Add a query sanitizer to the Redis instrumentation. This can be disabled
with the `sanitize_query = False` config option.

Given the query `SET key value`, the sanitized query becomes `SET ? ?`.
Both the keys and values are sanitized, as both can contain PII data.

The Redis queries are sanitized by default. This changes the default
behavior of this instrumentation. Previously it reported unsanitized
Redis queries.

This was previously discussed in the previous implementation of this PR
in PR open-telemetry#1571

Closes open-telemetry#1548

Changes suggested in
open-telemetry#1572 (comment)

The Redis test that performs the tests with the default options, doesn't
need to uninstrument and then instrument the instrumentor. This commit
removes the unnecessary setup code. The setup code is already present at
the top of the file.

- Update the sanitizer to also account for a max `db.statement`
  attribute value length. No longer than 1000 characters.
- Update the functional tests to assume the queries are sanitized by
  default.
- Add new tests that test the behavior with sanitization turned off.
  Only for the tests in the first test class. I don't think it's needed
  to duplicate this test for the clustered and async setup combinations.

Change the Redis functional tests so that they test the unsanitized
query by default, and test the sanitized query results in the separate
test functions.

This is a partial revert of the previous commit
8d56c2f

Update the Redis instrumentation library to not change the default
behavior for the Redis instrumentation. This can be enabled at a later
time when the spec discussion about this topic has concluded.

open-telemetry/opentelemetry-specification#3104

Remove else statement.

[ci skip]

Co-authored-by: Srikanth Chekuri <srikanth.chekuri92@gmail.com>

Check the length of the args array and return an empty string if there
are no args.

That way it won't cause an IndexError if the args array is empty and it
tries to fetch the first element, which should be the Redis command.