Fix Basic auth key encoding

[mariomac]

Fixes: #442

We weren't closing the encoder and sometimes we missed some bytes in the API key 😱

[grcevski]

LGTM!

[codecov-commenter]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (7ba3c5f) 78.32% compared to head (39da7d5) 65.96%.
Report is 1 commits behind head on main.

Files	Patch %	Lines
pkg/internal/export/otel/grafana.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #446       +/-   ##
===========================================
- Coverage   78.32%   65.96%   -12.37%     
===========================================
  Files          61       58        -3     
  Lines        5039     4933      -106     
===========================================
- Hits         3947     3254      -693     
- Misses        882     1412      +530     
- Partials      210      267       +57     

Flag	Coverage Δ
integration-test	65.96% <0.00%> (+0.12%)	⬆️
unittests	?

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[NiranjanHD]

@mariomac: I am looking at 401 Unauthorized errors in the latest release code [Beyla v1.2.1], am I missing anything?

ERROR: 2024/02/18 05:06:10 failed to upload metrics: failed to send metrics to https://otlp-gateway-prod-ap-south-1.grafana.net/otlp/v1/metrics: 401 Unauthorized

Grafana Beyla version used https://github.com/grafana/beyla/releases/download/v1.2.1/beyla-linux-amd64-v1.2.1.tar.gz

Reproducing error: followed steps mentioned in this link Grafana Beyla to upload OTEL traces to Grafana cloud which is static single instance agent basis.

[mariomac]

@NiranjanHD please check that, in the Grafana cloud API key, you are copying the raw API key and not the generated OTEL Headers ("Authorization: Basic ....").

As an alternative, try using the OTEL_EXPORTER_OTLP_HEADERS, as stated in the steps here:
https://grafana.com/docs/beyla/latest/quickstart/golang/#3-optional-get-grafana-cloud-credentials
https://grafana.com/docs/beyla/latest/quickstart/golang/#4-run-beyla-with-minimal-configuration