schema: add JSON schema for mcollective, migrator and mounts modules

[blackboxsw]

Proposed Commit Message

schema: add JSON schema for mcollective, migrator and mounts modules

Define static JSON schema for cloud-config modules in
cloudinit/config/cloud-init-schema.json. Migrate existing doc/examples
into inline meta schema examples where applicable.

Includes:
 - cc_mcollective
 - cc_migrator
 - cc_mounts

Doc drops:
 - doc/examples/cloud-config-mcollective.txt because example is included in
   inline meta schema docs

Additional Context

Test Steps

tox -re doc; xdg-open doc/rtd_html/topics/modules.html 
# validate visual changes vs https://cloudinit.readthedocs.io/en/latest/topics/modules.html#mcollective

# validate specific module rendered docs on cmdline
PYTHONPATH=. python3 -m cloudinit.cmd.main devel schema --docs cc_mcollective

Unit tests will run through any included cc_.meta['examples'] to confirm that they are correct schema.

Checklist:

• My code follows the process laid out in the documentation
• I have updated or added any unit tests accordingly
• I have updated or added any documentation accordingly

[TheRealFalcon]

Some comments inline, but overall looking good.

[TheRealFalcon]

String is valid here: https://github.com/canonical/cloud-init/blob/main/cloudinit/config/cc_mounts.py#L378-L381

[blackboxsw]

whoa nice find will add a positive example here in meta schema and fix this.

[blackboxsw]

added "pattern": "^([0-9]+)?\\.?[0-9]+[BKMGT]$"} to schema for swap.size swap.maxsize and unittests

[TheRealFalcon]

One typo we should fix, and everything else optional. For some reason Github wouldn't let me do suggestions on this review.

[TheRealFalcon]

Looks good!