Documentation: Add glossary for RWA vault and strategy allocation terminology

[Junirezz]

Define shared domain terms to keep engineering and product language aligned.

[Suzan-max]

@Suzan-max has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hi, I'd like to work on this issue. I've gone through the description and acceptance criteria and I'm confident I can deliver it. I'll make sure every acceptance criterion is met and submit a clean, tested PR. Please assign it to me.

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