Auto upgrade config files. (SYN-330)

[matrixbot]

For example, when we rename config options.

(Imported from https://matrix.org/jira/browse/SYN-330)

(Reported by @erikjohnston)

[matrixbot]

Jira watchers: @erikjohnston

[matrixbot]

Links exported from Jira:

is duplicated by SYN-329

[richvdh]

this seems a bit vague?

[ara4n]

i think this is asking for synapse to rewrite its yaml config files to add new options (or rename existing ones) when upgraded. obviously this has the minor problem that yaml doesn't let you do that and preserve formatting, plus users would probably be upset if it tried to do that without asking.

We definitely need to just package a default config file with the releases though so people can easily diff and see what's changed and manually incorporate the changes though...

[richvdh]

We definitely need to just package a default config file with the releases though so people can easily diff and see what's changed and manually incorporate the changes though...

Indeed, but that is #1433.

I'm not sure I'm keen on the premise of this bug as you explain it and am minded to close it.