[EXPORTER] Support URL-encoded values for OTEL_EXPORTER_OTLP_HEADERS

[pyohannes]

Fixes #2523

Changes

This PR adds support for URL-encoded values in OTEL_EXPORTER_OTLP_HEADERS and related headers, which is required by the specification.

The necessary url_decode function is added to ext/include/opentelemetry/ext/http/common/url_parser.h, which was renamed to ext/include/opentelemetry/ext/http/common/url_util.h to reflect the change.

For backwards compatibility, both URL-encoded and non-URL-encoded values are supported, for example:

OTEL_EXPORTER_OTLP_HEADERS="Authorization=Basic%20AAA"
OTEL_EXPORTER_OTLP_HEADERS="Authorization=Basic AAA"

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[marcalff]

Thanks for the fix.

Could we not rename url_parser.h to url_util.h ?

This will break user code, if there happens to be an include to url_parser.h, even when not used.

[pyohannes]

Could we not rename url_parser.h to url_util.h ?

@marcalff Got it, I reverted the renaming.

[marcalff]

LGTM, thanks for the fix.

[lalitb]

Thanks for the fix.