[java] Improve AvoidUsingOctalValues documentation

[oowekyala]

Is your feature request related to a problem? Please describe. The rule AvoidUsingOctalValues has no justification. The documentation

Integer literals should not start with zero since this denotes that the rest of literal will be interpreted as an octal value.

is vacuous, boiling down to "integer literals should not be octal literals since it denotes that the literal is octal". The message is even worse:

Do not start a literal by 0 unless it's an octal value

Good enough documentation would explain why octal literals should be avoided (being unusual is the only reason I can find though).

Describe the solution you'd like Rewrite the documentation and message of the rule.

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A clear and concise description of any alternative solutions or features you've considered.

Additional context
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