in_opentelemetry: Propogate tag in http2 metrics and trace handlers

[nuclearpidgeon]

For some reason whoever first wrote the in_opentelemetry plugin's HTTP/2 codepaths wrote it in a way that no/null tags were what always got passed into the Fluentbit routing engine. This PR fixes up what should be the last remaining cases not passing the tag through - the metrics and trace cases of the HTTP/2 codepath specifically. Should fully fix #8734 (i.e. fix it for the (default!) HTTP/2 mode and not force users to use the HTTP/1 codepath to get this behaviour).

Testing

• Example configuration file for the change attached

service:
    log_level: debug
pipeline:
    inputs:
        - name: opentelemetry
          tag_from_uri: true
          http2: true
    outputs:
        - name: 'stdout'
          match: 'v1_metrics'
        - name: 'stdout'
          match: 'v1_traces'

• Debug log output from testing the change attached
• Attached Valgrind output that shows no leaks or memory corruption was found

Documentation

• [N/A] Documentation required for this feature - No

Backporting

• This fix probably should be backported to the latest stable release, but it should probably get merged to master first.

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Fluent Bit is licensed under Apache 2.0, by submitting this pull request I understand that this code will be released under the terms of that license.

[nuclearpidgeon]

CC: @jpvallez