Use better type definitions for OT baggage module

[y9v]

What does this PR do?
This PR adds better type definitions for OpenTelemetry::Baggage from the file that was deleted in #5145.

Motivation:
This is a separate PR, since there was a small problem that was detected by steep and had to be fixed.

Change log entry
None.

Additional Notes:
None.

How to test the change?
CI.

[github-actions]

Typing analysis

Note: Ignored files are excluded from the next sections.

Untyped methods

This PR clears 1 untyped method and 4 partially typed methods. It increases the percentage of typed methods from 55.39% to 55.69% (+0.3%).

Untyped methods (+0-1)

✅ Cleared:

sig/datadog/opentelemetry/api/baggage.rbs:9
└── def clear: (?context: untyped) -> untyped

Partially typed methods (+0-4)

✅ Cleared:

sig/datadog/opentelemetry/api/baggage.rbs:11
└── def value: (String key, ?context: untyped) -> String?
sig/datadog/opentelemetry/api/baggage.rbs:13
└── def values: (?context: untyped) -> Hash[String, String]
sig/datadog/opentelemetry/api/baggage.rbs:15
└── def set_value: (String key, String value, ?metadata: String?, ?context: untyped) -> untyped
sig/datadog/opentelemetry/api/baggage.rbs:17
└── def remove_value: (String key, ?context: untyped) -> untyped

[datadog-official]

✅ Tests

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

🎯 Code Coverage
• Patch Coverage: 100.00%
• Overall Coverage: 95.23% (+0.00%)

View detailed report

_{This comment will be updated automatically if new data arrives.
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[ivoanjo]

👍 LGTM