docs: add providerId as a configuration option (#1567)

Signed-off-by: Michael Beemer <beeme1mr@users.noreply.github.com>

Author: beeme1mr

docs/reference/specifications/providers.md

@@ -280,6 +280,7 @@ Below are the supported configuration parameters (note that not all apply to bot
 | cache                 | FLAGD_CACHE                    | enable cache of static flags                                           | String - `lru`, `disabled`   | lru                           | rpc                     |
 | maxCacheSize          | FLAGD_MAX_CACHE_SIZE           | max size of static flag cache                                          | int                          | 1000                          | rpc                     |
 | selector              | FLAGD_SOURCE_SELECTOR          | selects a single sync source to retrieve flags from only that source   | string                       | null                          | in-process              |
+| providerId            | FLAGD_PROVIDER_ID              | A unique identifier for flagd(grpc client) initiating the request.     | string                       | null                          | in-process              |
 | offlineFlagSourcePath | FLAGD_OFFLINE_FLAG_SOURCE_PATH | offline, file-based flag definitions, overrides host/port/targetUri    | string                       | null                          | file                    |
 | offlinePollIntervalMs | FLAGD_OFFLINE_POLL_MS          | poll interval for reading offlineFlagSourcePath                        | int                          | 5000                          | file                    |
 | contextEnricher       | -                              | sync-metadata to evaluation context mapping function                   | function                     | identity function             | in-process              |