feat(guidelines): avoid digits in camelCase

[maxedenharter0507]

Changelog:

Update

• Specified that digits must be avoided when using camelCase notation in "MUST use camelCase for query parameters" R000022.
• Specified that digits must be avoided when using camelCase notation in "SHOULD use camelCase for property names" R004010.

[maxedenharter0507]

Feedback from the Async API Community: In general we agree on avoiding digits in camelCase. But we also thought about common abbreviations like B2B, B2C, and E2E, which are also used in our marketplace ecosystem. As we change the rule to “avoid digits” and not "disallow digits", this should be fine for such special cases.

We should disallow leading digits in property names, as this could lead to compile errors in common programming languages like Java.

[jensfischer1515]

LGTM, after adding more examples for DOs and DON'Ts