Added Weaver configuration for all telemetry, and a generated mkdocs site

[martinjt]

Changes

This adds a new service called telemetry-docs which serves a documentation site for the custom telemetry documented by the demo across all the services.

It also includes a weaver registry for the all those attributes.

This does not include a live-check interface, that will come later, nor does this include codegen for these attributes or metrics.

Merge Requirements

For new features contributions, please make sure you have completed the following
essential items:

• CHANGELOG.md updated to document new feature additions
• Appropriate documentation updates in the docs
• Appropriate Helm chart updates in the helm-charts

Maintainers will not merge until the above have been completed. If you're unsure
which docs need to be changed ping the
@open-telemetry/demo-approvers.

[julianocosta89]

@martinjt can we configure live-check to ensure the telemetry schema is always up to date?

I just don't want that to be another burden for maintainers.

Also, the k8s manifests shouldn't be part of this PR. That is generated via helm update whenever we have a new release

[martinjt]

We can, i just didnt want to make it part of this PR since its already got a lot of moving parts.

I can remove the k8s bits.