Prevent mutation of input options in all drivers

[jlucaso1]

Ensure that input options are not mutated across all drivers by creating a new options object from the input. This change enhances the integrity of the options passed to each driver.
Resolves #566

[43081j]

can you show us where we were mutating the options?

I wonder if we should treat them as read-only and then only clone them in places where we must mutate

since I suspect most drivers don't mutate, so can avoid having to allocate a new object and could let the TS compiler catch disallowed mutations (it'd need to be read-only deeply I suppose)

[pi0]

Typing input as readonly might be good idea I agree. there are also nested mutations possible (like push to array)

[43081j]

after hacking away at this a little, I think what we should do is just add read-only flags to our options types themselves

I was going to suggest introducing a DeepReadonly<T> and applying it to every opts parameter, but that feels like patching up the problem rather than solving it at the source

we could actually just change the various options types to already be readonly. for example:

export interface AzureKeyVaultOptions {
  readonly vaultName: string;
  readonly serviceVersion?: SecretClientOptions["serviceVersion"];
  readonly pageSize?: number;
}

a mutable object can be assigned to this as well as a read-only one, so it should be backwards compatible from the outside

and any types we expose which are not our own (e.g. SecretClientOptions here), we leave as-is. we don't try transform them into readonly as they're not our concern

any arrays would be ReadonlyArray<T>, and any nested objects would follow these same rules