Corrects internal_profiling.profile_dd_url config registration

[scottopell]

What does this PR do?

Fixes the way the config option internal_profiling.profile_dd_url is registered with configuration.

This config option (intentionally) does not set a default value, therefore the second argument to BindEnv was being treated as the name of the chose environment variable for this config option. In effect, the env var for this config option was "" (the empty string).

This makes it impossible to set this config option via environment variable.

Motivation

Was getting error when trying to set this config option via env var:

2023-03-13 18:31:13 EDT | CORE | WARN | (pkg/util/log/log.go:618 in func1) | Unknown environment variable: DD_INTERNAL_PROFILING_PROFILE_DD_URL

Additional Notes

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