[Storage/DynamoDB] Let vault modify dynamodb tables

[michael-diggin]

Description

Fixes Issue #25114.

This PR introduces support for creating the DynamoDB table that Vault would use with PAY_PER_REQUEST billing mode, and introduces support for allowing Vault to modify the billing mode and read/write capacity of the table if it already exists. This is done with new environment variables, and the current default behaviour is left unchanged (no-ops if the table already exists).

cc @schavis, @VioletHynes

[michael-diggin]

cc @VioletHynes here is the new PR :)

[VioletHynes]

Looks good! Thanks again :)

[michael-diggin]

These failures don't seem related to my changes if I understand correctly.
eg failing to install docker in the GH action https://github.com/hashicorp/vault/actions/runs/12875984251/job/35898853797?pr=29371#step:13:58
or proto files being different https://github.com/hashicorp/vault/actions/runs/12875984241/job/35898823559?pr=29371#step:5:324
Is there anything I can do/change in my PR to fix these checks?

[VioletHynes]

Yeah, I'm looking into the CI failures. They're unrelated to your changes and failing elsewhere too. I'll try and get it fixed then merge it into this branch. Appreciate your patience!

[michael-diggin]

Ah no worries, thanks for looking into it!

[VioletHynes]

Okay, CI issue fixed and everything's passing. I just need a re-review from the docs team, but this should be ready to go soon :)

[michael-diggin]

Ah amazing thank you for reviewing and seeing this through @VioletHynes!