feat(instrumentation-ioredis): add requireParentSpan option to config

[blumamir]

Which problem is this PR solving?

• fixes ioredis: add requireParent config option #344
• As discussed in the issue, I've implemented this option so there is no behavior change from how instrumentation is currently operating. This PR does not normalize the requiredParent behavior with other plugins which have different defaults.
• The new config option name is requiredParentSpan, as suggested by @obecny .

Short description of the changes

• added requiredParentSpan to instrumentation config, and skip instrumentation only if this config option was set to false.
• I have added unittests for both cases (true and false). existing tests are verifying the behavior when this config option is unset.
• I added the new config option and description to the instrumentation README.md

[codecov]

Codecov Report

Merging #372 (f9fc91a) into main (e3c1359) will not change coverage.
The diff coverage is n/a.

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