This patch fixes parsing of the `max_lsn_wal_lag` tenant config item.
We were incorrectly expecting a string before, but the type is a
NonZeroU64.
So, when setting it in the config, the (updated) test case would fail
with
```
E psycopg2.errors.InternalError_: Tenant a1fa9cc383e32ddafb73ff920de5f2e6 will not become active. Current state: Broken due to: Failed to parse config from file '.../repo/tenants/a1fa9cc383e32ddafb73ff920de5f2e6/config' as pageserver config: configure option max_lsn_wal_lag is not a string. Backtrace:
```
So, not even the assertions added are necessary.
The test coverage for tenant config is rather thin in general.
For example, the `test_tenant_conf.py` test doesn't cover all the
options.
I'll add a new regression test as part of attach-time-tenant-conf PR
https://github.com/neondatabase/neon/pull/4255
4d41b2d379