fix: Update documentation for using filename in otelcol.auth.bearer c…

…omponent (#2213)

* Add documentation for filename usage

* Update docs/sources/reference/components/otelcol/otelcol.auth.bearer.md

Co-authored-by: Clayton Cornell <[email protected]>

---------

Co-authored-by: William Dumont <[email protected]>
Co-authored-by: Clayton Cornell <[email protected]>

docs/sources/reference/components/otelcol/otelcol.auth.bearer.md

@@ -40,6 +40,10 @@ Name     | Type     | Description                                      | Default
 When sending the token, the value of `scheme` is prepended to the `token` value.
 The string is then sent out as either a header (in case of HTTP) or as metadata (in case of gRPC).
 
+If you use a file to store the token, you can use `[local.file`][local.file] to retrieve the `token` value from the file.
+
+[local.file]: ../../local/local.file/
+
 ## Blocks
 
 The following blocks are supported inside the definition of
@@ -97,7 +101,7 @@ otelcol.auth.bearer "creds" {
 
 The example below configures [otelcol.exporter.otlphttp][] to use a bearer token authentication.
 
-If we assume that the value of the `API_KEY` environment variable is `SECRET_API_KEY`, then 
+If we assume that the value of the `API_KEY` environment variable is `SECRET_API_KEY`, then
 the `Authorization` HTTP header is set to `MyScheme SECRET_API_KEY`.
 
 ```alloy