Create schema on update if it does not exist

Makes the `cmgr update-schema` subcommand and cmgrd
`POST /schemas/{schema_name}` function like upserts
rather than updates. If the named schema does not
exist, a warning will be logged and the schema will
be created, rather than returning an error.

This allows clients to call `update-schema` without the
need to know whether a given schema has already been
created or not, without needing to handle nonexistent
schema errors and falling back to `add-schema`.

Merge branch 'dev'

Fix security advisory

Update docker dependencies

Fixes documentation discrepancy

Updates the behavior of `updateChallengeInfo` to match the documented
behavior of defaulting to `CMGR_DIR` (or `.` if not explicitly set).

Fixes ArmyCyberInstitute#34