docs: Describe token locality for auth methods

[eculver]

Summary

I took a stab at adding a "Token Locality" section to the Auth Method docs. I hope this makes sense, but the topic is rather nuanced and consequently, I found difficult to describe.

Details

By default, auth methods create locally scoped tokens. Auth Methods can be configured to create globally scoped tokens, but there are a number of nuanced restrictions around the behavior. This PR attempts to document such things by adding a "Token Locality" section to the root Auth Method docs and then linking to the specifics in the docs about individual Auth Methods.

Note: I think I got this right, but I am honestly not sure if I covered everything. If there are suggestions as to how to describe the "alternative" approach using the anonymous token, please share; this is one part of the change I was least sure of.

TODO

• [ ] update index to introduce -token-locality flag as Adam suggested
• [ ] apply any/all suggestion about Kubernetes docs
• [ ] link to anonymous token docs
• [ ] add part about anonymous token that Luke mentioned here
• [ ] add Luke’s suggestion to k8s docs

[hashicorp-cla]

All committers have signed the CLA.

[github-actions[bot]]

This pull request has been automatically flagged for inactivity because it has not been acted upon in the last 60 days. It will be closed if no new activity occurs in the next 30 days. Please feel free to re-open to resurrect the change if you feel this has happened by mistake. Thank you for your contributions.

[github-actions[bot]]

Closing due to inactivity. If you feel this was a mistake or you wish to re-open at any time in the future, please leave a comment and it will be re-surfaced for the maintainers to review.