Regenerate client & test more example

[mstruebing]

• Updated setting to match newer gen and openapi-generator versions
• Regenerated the client with [Bug] fix: use length to check for default return media type OpenAPITools/openapi-generator#15833 applied
• Fixed a type issue after regenerating the client
• tested more examples and updated FETCH_MIGRATION.md accordingly, updated examples to easier change related properties (namespace, podnames, etc.)

Can be reviewed as individual commits if the full diff is to big.

• Closes [release-1.x] getPreferredMediaType doesn't handle empty arrays resulting in None of the given media types are supported: #1075
• Closes [release-1.x] Fix media type error #1120

FYI: I created an upstream PR in node-fetch but I do not know if this will get accepted: node-fetch/node-fetch#1757

[brendandburns]

Nice, thank you!

/lgtm
/approve

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