Update analytics middleware to log requests lacking a `user-agent` header

[eecavanna]

Description

The changes on this branch make it so the analytics middleware no longer raises a KeyError when the incoming request lacks a user-agent (case-insensitive) header.

If someone wants the runtime to deny those requests, I propose that be done elsewhere (and explicitly documented).

Fixes #515.

Type of change

• [x] Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

I confirmed, locally (shown here), that requests that lack a User-Agent header are now logged by the analytics middleware. I also confirmed that requests that have the header are also logged (as they were before).

Configuration Details: none

Checklist:

• [x] My code follows the style guidelines of this project (have you run black nmdc_runtime/?)
• [x] I have performed a self-review of my code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation (in docs/ and in https://github.com/microbiomedata/NMDC_documentation/?)
• [x] I have added tests that prove my fix is effective or that my feature works, incl. considering downstream usage (e.g. https://github.com/microbiomedata/notebook_hackathons) if applicable.
• [x] New and existing unit and functional tests pass locally with my changes (make up-test && make test-run)

[eecavanna]

I will test this change locally now—to confirm putting a value of None in that property of the dictionary doesn't break anything downstream.

[eecavanna]

I confirmed, locally (shown here), that requests that lack a User-Agent header are now logged by the analytics middleware. I also confirmed that requests that have that header are also logged (as they were before).

[eecavanna]

Hi @shreddd, I finished testing this branch.