in_opentelemetry: support tag_from_uri

[nokute78]

This patch is to support property tag_from_uri.

Currently, in_otel composes tag from uri.
e.g. v1_metrics, v1_traces or v1_logs.

It may confuse user. #7939

If user set tag_from_uri=false, tag will be the value of property tag.
Default is true to prevent breaking current behavior.

Key	Description	Default
tag_from_uri	If true, tag will be created from uri. e.g. v1_metrics from /v1/metrics .	true

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Enter [N/A] in the box, if an item is not applicable to your change.

Testing
Before we can approve your change; please submit the following in a comment:

• Example configuration file for the change
• Debug log output from testing the change

• Attached Valgrind output that shows no leaks or memory corruption was found

If this is a change to packaging of containers or native binaries then please confirm it works for all targets.

• [N/A] Run local packaging test showing all targets (including any new ones) build.
• [N/A] Set ok-package-test label to test for all targets (requires maintainer to do).

Documentation

• Documentation required for this feature

Backporting

• [N/A] Backport to latest stable release.

Configuration

[INPUT]
    Name opentelemetry
    Tag not_uri
    Tag_from_uri false

[OUTPUT]
    Name stdout
    Match *

Debug/Valgrind output

Use curl like

curl --header "Content-Type: application/json" --request POST --data '{"resourceLogs":[{"resource":{},"scopeLogs":[{"scope":{},"logRecords":[{"timeUnixNano":"1660296023390371588","body":{"stringValue":"{\"message\":\"dummy\"}"},"traceId":"","spanId":""}]}]}]}'   http://0.0.0.0:4318/v1/logs

$ valgrind --leak-check=full bin/fluent-bit -c a.conf 
==10939== Memcheck, a memory error detector
==10939== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==10939== Using Valgrind-3.18.1 and LibVEX; rerun with -h for copyright info
==10939== Command: bin/fluent-bit -c a.conf
==10939== 
Fluent Bit v2.2.0
* Copyright (C) 2015-2023 The Fluent Bit Authors
* Fluent Bit is a CNCF sub-project under the umbrella of Fluentd
* https://fluentbit.io

[2023/11/04 09:15:32] [ info] [fluent bit] version=2.2.0, commit=99d568b7c1, pid=10939
[2023/11/04 09:15:32] [ info] [storage] ver=1.2.0, type=memory, sync=normal, checksum=off, max_chunks_up=128
[2023/11/04 09:15:32] [ info] [cmetrics] version=0.6.4
[2023/11/04 09:15:32] [ info] [ctraces ] version=0.3.1
[2023/11/04 09:15:32] [ info] [input:opentelemetry:opentelemetry.0] initializing
[2023/11/04 09:15:32] [ info] [input:opentelemetry:opentelemetry.0] storage_strategy='memory' (memory only)
[2023/11/04 09:15:32] [ info] [input:opentelemetry:opentelemetry.0] listening on 0.0.0.0:4318
[2023/11/04 09:15:32] [ info] [output:stdout:stdout.0] worker #0 started
[2023/11/04 09:15:32] [ info] [sp] stream processor started
[0] not_uri: [[1660296023.1698112429, {}], {"log"=>"{"message":"dummy"}"}]
^C[2023/11/04 09:15:35] [engine] caught signal (SIGINT)
[2023/11/04 09:15:35] [ warn] [engine] service will shutdown in max 5 seconds
[2023/11/04 09:15:35] [ info] [engine] service has stopped (0 pending tasks)
[2023/11/04 09:15:35] [ info] [output:stdout:stdout.0] thread worker #0 stopping...
[2023/11/04 09:15:35] [ info] [output:stdout:stdout.0] thread worker #0 stopped
==10939== 
==10939== HEAP SUMMARY:
==10939==     in use at exit: 0 bytes in 0 blocks
==10939==   total heap usage: 1,605 allocs, 1,605 frees, 1,243,678 bytes allocated
==10939== 
==10939== All heap blocks were freed -- no leaks are possible
==10939== 
==10939== For lists of detected and suppressed errors, rerun with: -s
==10939== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

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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.

[nokute78]

Doc PR is fluent/fluent-bit-docs#1275