The viper automatic env mapping and BindEnv were both creating mappings
like `vip.BindEnv("telemetry", "CODER_TELEMETRY")` which we don't want
since `DeploymentConfig.Telemetry` is a struct housing fields.
For some reason, this was causing `DeploymentConfig.Telemetry.URL` to
**not** be assigned its default value when `CODER_TELEMETRY=false` was
set as an environment variable.
Potentially we would want `"telemetry.enable"` to be mapped to
`"CODER_TELEMETRY"` for simplicity. But that behavior is not changed by
this commit.
Arguably, we could remove `vip.SetEnvPrefix` and `vip.SetEnvKeyReplacer`
as well since we're manually controlling all environment variable names
via `formatEnv`.