[Feature Request] API key client option

[cretz]

Describe the solution you'd like

Every place that creates a client (nay a connection) should have an option to accept an API key which becomes the Authorization header of Bearer <api-key>. This is commonly used in self-hosted setups and will become common for cloud.

Client places:

• Go - API key client option sdk-go#1401
• CLI (after Go) - CLI Refresh: API key client option cli#478
• Java - API key client option sdk-java#1997
• Core - [Feature Request] API key client option sdk-core#695
• TypeScript (after Core) - [Feature Request] API key client option sdk-typescript#1367
• Python (after Core) - [Feature Request] API key client option sdk-python#482
• .NET (after Core) - [Feature Request] API key client option sdk-dotnet#191
• PHP - [Feature Request] API key client option sdk-php#410

Thought was given to whether this should be lang only or core, but it became clear that "rpc metadata" (aka gRPC metadata aka headers) should remain separate from this setting all the way until headers are actually applied because people copy this client config in other places and it shouldn't just be a shallow alias for setting RPC metadata at that level.

[tlalfano]

Do we need to add PHP to the list here? @cretz

[cretz]

@tlalfano - yes, I just added it