Ignore non-utf8 characters

[tianchu]

What does this PR do?

Sometimes the log content from s3 object may contain characters that are not encoded in utf-8, and it would cause the Forwarder to error like UnicodeDecodeError: 'utf-8' codec can't decode byte 0xfd in position 115924522: invalid start byte. This PR makes the Forwarder to ignore the invalid or non-decodable characters, and therefore it doesn't error and still forward the rest of the logs that are valid.

Motivation

Testing Guidelines

Additional Notes

Types of changes

• Bug fix
• New feature
• Breaking change
• Misc (docs, refactoring, dependency upgrade, etc.)

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