add docs for logtag

Author: quinnj

docs/src/client.md

@@ -107,6 +107,10 @@ When a non-2XX HTTP status code is received in a response, this is meant to conv
 
 If `true`, `HTTP.StatusError`, `HTTP.TimeoutError`, `HTTP.IOError`, and `HTTP.ConnectError` will be logged via `@error` as they happen, regardless of whether the request is then retried or not. Useful for debugging or monitoring requests where there's worry of certain errors happening but ignored because of retries.
 
+### `logtag`
+
+If provided, will be used as the tag for error logging. Useful for debugging or monitoring requests.
+
 ### `observelayers`
 
 If `true`, enables the `HTTP.observelayer` to wrap each client-side "layer" to track the amount of time spent in each layer as a request is processed. This can be useful for debugging performance issues. Note that when retries or redirects happen, the time spent in each layer is cumulative, as noted by the `[layer]_count`. The metrics are stored in the `Request.context` dictionary, and can be accessed like `HTTP.get(...).request.context`.

src/HTTP.jl

@@ -158,6 +158,7 @@ Supported optional keyword arguments:
  - `logerrors = false`, if `true`, `HTTP.StatusError`, `HTTP.TimeoutError`, `HTTP.IOError`, and `HTTP.ConnectError` will be
     logged via `@error` as they happen, regardless of whether the request is then retried or not. Useful for debugging or
     monitoring requests where there's worry of certain errors happening but ignored because of retries.
+ - `logtag = nothing`, if provided, will be used as the tag for error logging. Useful for debugging or monitoring requests.
  - `observelayers = false`, if `true`, enables the `HTTP.observelayer` to wrap each client-side "layer" to track the amount of
    time spent in each layer as a request is processed. This can be useful for debugging performance issues. Note that when retries
    or redirects happen, the time spent in each layer is cumulative, as noted by the `[layer]_count`. The metrics are stored