Lambda `Function` update code path

[a-hilaly]

Currently the Lambda controller only supports create and delete operations. We should add Update operation code path as well.

• Add ReservedConurrentExecutions field from PutFunctionConcurrency operation
• Add CodeSigningConfig field from PutFunctionCodeSigningConfig
• Move Layers to Spec fields
• Custom update function
• e2e tests for update operations
• Hooks and e2e for Image based Lambda functions

/assign