event_logs: instrument SOAP-related event logs

[unknwon]

This PR adds instruments for SOAP-related event logs, including:

1. All GraphQL requests (both the cookie or access token authenticated) are logged for SOAP users.
2. All event logs and security event logs are attributed with "sourcegraph_operator": true in the public_argument and argument columns respectively.

Below are the captures of event logs that we want in both event_logs and security_event_logs tables:

Test plan

1. Create a temporary JSON file (site-config.json) with the following content, the credentials can be obtained from the "Okta test instance admin" in 1Password and the "OpenID Connect (sourcegraph.test:3443)" application:

   {
     "authProviders": {
       "sourcegraphOperator": {
         "issuer": "https://dev-433675.oktapreview.com",
         "clientID": "<REDACTED>",
         "clientSecret": "<REDACTED>",
         "lifecycleDuration": 60
       }
     }
   }

2. Save the "Sourcegraph Cloud site config singer key" in 1Password to a temporary file (singer.key), and use it to sign the site config:

   go run enterprise/internal/cloud/sign_site_config.go -private-key singer.key  -site-config site-config.json

3. Set the output of the above command as the value of the env var SRC_CLOUD_SITE_CONFIG
4. Comment out the "licenseKey" from the dev-private/enterprise/dev/site-config.json
5. Boot up the local Sourcegraph instance and try to sign in with "Sourcergaph Operators" using the same Okta account used in step 1.
6. Entries generated in event_logs and security_event_logs are attributed with "sourcegraph_operator": true in public_argument and argument columns respectively.

---

Stacked on https://github.com/sourcegraph/sourcegraph/pull/44200, closes https://github.com/sourcegraph/customer/issues/1428

[sourcegraph-bot]

Codenotify: Notifying subscribers in CODENOTIFY files for diff e8a9c9c...2a5b04e.

Notify	File(s)
@keegancsmith	cmd/frontend/graphqlbackend/search_test.go
@rvantonder	cmd/frontend/graphqlbackend/search_test.go

[unknwon]

@sourcegraph/iam Please take this as a soft review request, because I don't know who else to tag 😁

[michaellzc]

followed the test plan and it worked for me

code changes LGTM

[unknwon]

On dotcom with 34000+ rows in the user_external_accounts, this query takes ~10ms (with no result, since SOAP users are very rare), just as a data point. I think it is acceptable for now.

If this becomes a problem, we could store whether a user is created by SOAP in Redis to reduce the number of direct DB queries. Or very dumb in-memory cache within the frontend.

[unknwon]

Merging as-is, post-merge comments are welcome (as always) and will address them once I'm back from PTO (Nov 28th)!