chore: upgrade base-server to 1.15.7 and base-builder to 1.14.8

[robcao]

What was changed

I upgraded the temporalio/base-server image to 1.15.7, and the temporalio/base-builder image to 1.14.8.

Why?

I did this to match what was in the docker builds repository.

It looks like base server image is several months old, and as a result, had accumulated some vulnerabilities over time. The purpose of this pull request is to upgrade the base image to resolve most of the vulnerabilities.

Checklist

1. Closes

2. How was this tested:

I built the docker image locally and compared the vulnerabilities.

before with 2.25.0

now

3. Any docs updates needed?

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