Switch golang.org/x/crypto to gravitational fork

[jakule]

This PR switches Teleport from using golang.org/x/crypto to our internal fork github.com/gravitational/crypto to work around the issue with OpenSSH < 7.6.
Recently, Go crypto added support for OpenSSH 8.5+ golang/crypto@6fad3df, but they also broke the older OpenSSH compatibility. Our fork works with older and "modern" OpenSSH, including this gravitational/crypto@903e656 change (not yet available upstream).

Closes #10918
Closes #17197
Closes #17046

[hatched]

Do we have an issue somewhere to track reverting this change once this issue has been resolved upstream?

[jakule]

@fspmarshall Friendly ping.

[zmb3]

cc @rosstimothy for awareness - we'll have to keep our fork up to date as upstream changes

[rosstimothy]

Does this change allow us to update dependencies which in turn depend on > x/crypto v0.2.0?

[codingllama]

Could you update the following files as well?

• api/go.mod -> needs the same replace as base go.mod, and it has the same "do not update" warning (https://github.com/gravitational/teleport/blob/master/api/go.mod#L32-L36).

• .github/dependabot.yml -> please move crypto to the forked/replaced section (https://github.com/gravitational/teleport/blob/master/.github/dependabot.yml#L19), for both go.mod and api/go.mod entries.

[jakule]

Does this change allow us to update dependencies which in turn depend on > x/crypto v0.2.0?

@rosstimothy Yes, with this change, we can use x/crypto HEAD.

[codingllama]

Could you update the following files as well?

• api/go.mod -> needs the same replace as base go.mod, and it has the same "do not update" warning (https://github.com/gravitational/teleport/blob/master/api/go.mod#L32-L36).
• .github/dependabot.yml -> please move crypto to the forked/replaced section (https://github.com/gravitational/teleport/blob/master/.github/dependabot.yml#L19), for both go.mod and api/go.mod entries.

Missing dependabot.yml?

[jakule]

@codingllama Sorry, I missed that. Fixed 981e541