better error message for context token generation

[shazron]

Right now, if your context does not support the properties needed for the OAuth, or JWT IMS plugins, it will show this error:
Error: cannot generate token because no plugin supports configuration

This error is not very descriptive. There is more info when prefixing this environment variable DEBUG=@adobe/aio-lib-ims:token-helper before your command.

The IMS plugins do check for missing keys, and we can expose the missing keys in aio-lib-ims for reporting: https://github.com/adobe/aio-lib-ims-jwt/blob/f5028aa800c41f53aac663c4ccdcbae4c672263c/src/ims-jwt.js#L39

The issue is, if it is missing properties for a plugin, that's ok, it can match for another plugin. If it does not match all plugins, we need to print out the error message for all the plugins (missing key(s)), so the user can see and filter for themselves.

Expected

When an ims context does not match any IMS plugin, this error is shown:

context properties: ['...']
@adobe/aio-lib-ims-jwt: missing keys(s) ['private_key']
@adobe/aio-lib-ims-oauth: missing keys(s) ['scope', 'redirect_uri' ]

Actual

When an ims context does not match any IMS plugin, this error is shown:
Error: cannot generate token because no plugin supports configuration

[aiojbot]

JIRA issue created: https://jira.corp.adobe.com/browse/ACNA-1147