feat: Add implementation state (amend)

[HazAT]

Many RFCs are in a state where meaningful feedback only occurs once we start to implement them. So after we wrote it, asked for feedback etc.

We miss a forcing function for people to think about the problem to have a strong opinion about a topic.

This doesn't apply to every RFC, but it's a recurring theme, especially in SDKs and topics around APIs.
And I don't want to blame anyone here, I think this is mostly how people work - but I feel it's annoying and adds unnecessary friction.
The person driving RFCs also feels it when this happens that they haven't gotten any meaningful feedback yet.

That's why I am proposing to add a new RFC state called implementation

FAQ:

Why can't it stay in draft?
The RFC is still not approved so it's a draft, though the implementation state really is a forcing function for the author to move forward and also demonstrates more maturity than just draft

Should we just have a sync meeting with the people involved to come to a conclusion?
Nothing beats actually writing the code and seeing where it falls short, sync meetings where everyone says LGTM won't solve it.

Can we create a Github Project or Workflow to cover this case instead?
That's too much complexity for everyone to keep track of and maintain.

Why are POCs not solving this?
POCs for changes are definitely welcome and help a lot but often are not enough to get feedback from different teams or people. Only when it gets serious and people make it their problem to solve they have opinions about it.

Will this new state fix my entire life?
No

[AbhiPrasad]

Feel free to amend https://github.com/getsentry/rfcs/blob/main/text/0101-revamping-the-sdk-performance-api.md to be implementation. Thanks!