Automate deprecated variable removal

[dragonchaser]

We have introduced a method to mark variables as deprecated and removal in our code like:

// Reva defines all available REVA client configuration.
type Reva struct {
	Address string        `yaml:"address" env:"OCIS_REVA_GATEWAY;REVA_GATEWAY" desc:"The CS3 gateway endpoint." deprecationVersion:"3.0" removalVersion:"4.0.0" deprecationInfo:"REVA_GATEWAY changing name for consistency" deprecationReplacement:"OCIS_REVA_GATEWAY"`
	TLS     GRPCClientTLS `yaml:"tls"`
}

this came in handy when removing the variables for 4.0.0 (see #7099). I just realized that removing all the variables from the seperate config.go files is an effort that could be automated.

I suggest we write a small tool that will patch this code automatically

Workflow:

$> ./deprecation_helper <version>

This will remove all the variables and deprecation annotations from the code in the config.go files and will just leave us with the actual occurrences in the code, thus reducing the workload that is actually needed to remove those variables (pressing delete hundreds of time is just a waste of precious time). It would also be helpful to add an additional helper function to that tool that would point to locations where those variables are used directly through os.GetEnv() or occur in static strings etc.

Addiotional (needed) functionality:

• Whenever a variable is removed, it needs to be written to a (text-)database
• Upon startup ocis checks for the contents of the database, and checks if the variables are set
• if one of the variables is still set, ocis will refuse to start up
• deprecated variables should also be added to this database and create a log output if set upon startup
• if there are deprecated or removed variables still set, admin (ui admin, not sysadmin) should see a toast in the ui hinting the person to contact the sysadmin to check the config
• Note: These database(s) need to bee added to the git-repo and need to be bundled upon build!

/cc @kobergj @mmattel

[mmattel]

This is an important functionality we should asap build to relax tasks when a new major release is coming. Please prioritize.

[stale]

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