Log-only sources can't output metrics with the influxdb decoder

[jorgehermo9]

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Problem

As discussed in #21027, log-only sources (for example, the exec source) should be capable of emitting metrics with a decoder that does not include logs in its output (currently, the influxdb decoder is the only one with this behavior).

Configuration

sources:
  file:
    type: exec
    command: ["cat", "sampling.txt"]
    decoding:
      codec: "influxdb"
    mode: streaming
sinks:
  console:
    type: console
    inputs: ["file"]
    encoding:
      codec: "json"

Version

vector 0.40.0 (x86_64-unknown-linux-gnu)

Debug Output

2024-08-10T09:58:45.063500Z DEBUG vector::app: Internal log rate limit configured. internal_log_rate_secs=10
2024-08-10T09:58:45.063519Z  INFO vector::app: Log level is enabled. level="trace"
2024-08-10T09:58:45.063538Z DEBUG vector::app: messaged="Building runtime." worker_threads=20
2024-08-10T09:58:45.064633Z  INFO vector::app: Loading configs. paths=["config.yaml"]
2024-08-10T09:58:45.066867Z DEBUG vector::config::loading: No secret placeholder found, skipping secret resolution.
thread 'main' panicked at lib/vector-core/src/config/mod.rs:128:9:
assertion failed: ty.contains(DataType::Log)
stack backtrace:
   0:     0x6081905123a5 - <unknown>
   1:     0x60819054364b - <unknown>
   2:     0x60819050c57f - <unknown>
   3:     0x60819051217e - <unknown>
   4:     0x608190513c79 - <unknown>
   5:     0x6081905139bd - <unknown>
   6:     0x608190514113 - <unknown>
   7:     0x608190513fbb - <unknown>
   8:     0x608190512869 - <unknown>
   9:     0x608190513d27 - <unknown>
  10:     0x60818b96b9b3 - <unknown>
  11:     0x60818b96ba5c - <unknown>
  12:     0x60818f4e671b - <unknown>
  13:     0x60818bbc35d7 - <unknown>
  14:     0x60818c639b24 - <unknown>
  15:     0x60818bfaae47 - <unknown>
  16:     0x60818c55561f - <unknown>
  17:     0x60818c550ec9 - <unknown>
  18:     0x60818df6b284 - <unknown>
  19:     0x60818df8cff6 - <unknown>
  20:     0x60818df006d9 - <unknown>
  21:     0x60818c4a840f - <unknown>
  22:     0x60818d667608 - <unknown>
  23:     0x60818d667059 - <unknown>
  24:     0x60818d666d91 - <unknown>
  25:     0x60818d666c49 - <unknown>
  26:     0x60818b96f082 - <unknown>
  27:     0x60818b96f3f6 - <unknown>
  28:     0x60818b96f40c - <unknown>
  29:     0x6081905011c0 - <unknown>
  30:     0x60818b96f2d4 - <unknown>
  31:     0x76ac681a2e08 - <unknown>
  32:     0x76ac681a2ecc - __libc_start_main
  33:     0x60818b96df45 - <unknown>
  34:                0x0 - <unknown>

Example Data

No response

Additional Context

No response

References

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