Bump version to 2.2.0

[jrothrock]

Minor release for #119, #120 and #118.

• Bump ScoutApm::Logging::VERSION to 2.2.0
• Turn the Unreleased section of CHANGELOG.md into 2.2.0 and add entries for fix: write log text that isn't valid UTF-8 instead of raising #120 and Add release workflow for RubyGems trusted publishing #118

What's in it:

• Remove severity-number exporter patch; map severity at emit time #119: severity numbers are correct again with opentelemetry-exporter-otlp-logs >= 0.7.0, the OTLP exporter monkey patch is gone, and logger.unknown no longer raises.
• fix: write log text that isn't valid UTF-8 instead of raising #120: log text that isn't valid UTF-8 is written with the bad bytes replaced instead of raising. Thanks @rpearce!
• Add release workflow for RubyGems trusted publishing #118: release workflow for publishing to RubyGems with trusted publishing.

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