feat(storage): add support for object context

[shubhangi-google]

This pull request introduces new functionality to the Google::Cloud::Storage::File class, enabling direct manipulation of an object's context. This enhancement provides greater control over file metadata, facilitating more nuanced data management within Google Cloud Storage.

Highlights

• Object Contexts Support: Introduced comprehensive support for Google Cloud Storage Object Contexts, allowing users to attach custom key-value pairs to objects for enhanced metadata management.
• Listing and Filtering: Added the ability to filter object listings based on Object Contexts, supporting queries for presence, absence, existence, and non-existence of specific context keys or key-value pairs.
• Input Validation: Implemented validation to prevent the use of forbidden characters (double quotes) in Object Context keys and values, ensuring compatibility with GCS filter string syntax.
• System and Unit Tests: Expanded test coverage with new system and unit tests to verify the functionality of Object Contexts across various scenarios, including creation, updates, copying, combining, and filtering.

[snippet-bot]

Here is the summary of changes.

You are about to add 3 region tags.

• google-cloud-storage/samples/storage_get_object_contexts.rb:17, tag storage_get_object_contexts
• google-cloud-storage/samples/storage_list_object_contexts.rb:17, tag storage_list_object_contexts
• google-cloud-storage/samples/storage_set_object_contexts.rb:17, tag storage_set_object_contexts

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[aandreassa]

Temporarily adding label. We can remove next week