Streamlining of "Admin API" wording

[JOJ0]

A low priority cosmetic thing:

We used to state "admin API" throughout.

Since AFAIK Synapse docs, at some point, have been changed to use "Admin API", we should streamline and use that wording/capitalization as well.

[JacksonChen666]

also, being more specific like "synapse admin API" is better than just "admin API" because the synapse admin API is specific to synapse and nothing else (dendrite, conduit, etc.)

[JOJ0]

In some places adding Synapse might be ok (and we often have that), in others leaving it out is the way to go because it's crystal clear already that we are talking about Synapse and repeating the word again doesnt help readability.

Mainly I'm talking about capitalization of the word Admin here anyway - it should be the same everywhere. When I started out writing this tool I tried to make sure I use lower case like Synapse docs used. That changed since then....they now start with a capital A.