[containerd-config-toml] set default runtime_type value if not present

[tariq1890]

Fixes #1956

This PR addresses a scenario where valid albeit incomplete containerd config tomls may be provided as a base config. In this case, the runtime_type field was missing in the base config TOML, so the drop-in config TOML which defines the custom runtimes did not have the runtime_type populated. This led to errors starting up containers which used these custom runtimes.

error="rpc error: code = InvalidArgument desc = failed to start sandbox \"96ca033f576080a5cbf8365e57fad83184c690fd17ea9ffc3fa3c4bf8c6b220e\": failed to create containerd container: create container failed validation: container.Runtime.Name must be set: invalid argument"

This PR changes that by automatically populating the runtime_type field with the default value in the new runtime handler blocks should the runtime_type be empty

[coveralls]

Coverage Report for CI Build 30931930163

Coverage increased (+0.01%) to 43.626%

Details

• Coverage increased (+0.01%) from the base build.
• Patch coverage: 3 of 3 lines across 1 file are fully covered (100%).
• No coverage regressions found.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	15266
Covered Lines:	6660
Line Coverage:	43.63%
Coverage Strength:	0.49 hits per line

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💛 - Coveralls