Support Ubuntu 22.04 for Swift 5.7

[shahmishal]

• Add Docker image for Ubuntu 22.04 on swift-docker repo
• Add Swift CI jobs to build nightly toolchains
• Update the automation to include Ubuntu 22.04 toolchain
• Update the website to include links to Ubuntu 22.04

[shahmishal]

Currently, the release/5.7 does not contain all of the Python 3 changes required to support Ubuntu 22.04.

To support Python 3 we will need to merge following pull requests:

• [5.7] Use collections.abc.Iterable instead of collection.Iterable #60408
• [5.7] Use Python 3 #60452
• [5.7] Migrate to use Python 3 swift-syntax#564

[neilt]

Can't wait, we are moving our test servers to 22.04.

[shahmishal]

swiftlang/swift-llbuild#838

[shahmishal]

swiftlang/swift-package-manager#5743

[shahmishal]

swiftlang/indexstore-db#157

[shahmishal]

swiftlang/sourcekit-lsp#616

[shahmishal]

swiftlang/swift-docc#370

[shahmishal]

swiftlang/swift-org-website#126

[shahmishal]

Ubuntu 22.04 now available on swift.org for nightly snapshots.