Use ClientConfig from pg

[brandonchinn178]

Just use ClientConfig from pg instead of defining it explicitly. Getting a type error, since the ssl field in ClientConfig from pg is slightly different from the ssl field in here.

Type 'ClientConfig' is not assignable to type 'string | ClientConfig'.
  Type 'import(".../node_modules/@types/pg/index").ClientConfig' is not assignable to type 'import(".../node_modules/node-pg-migrate/dist/types").ClientConfig'.
    Types of property 'ssl' are incompatible.
      Type 'boolean | ConnectionOptions | undefined' is not assignable to type 'boolean | TlsOptions | undefined'.
        Type 'ConnectionOptions' is not assignable to type 'boolean | TlsOptions | undefined'.
          Type 'ConnectionOptions' is not assignable to type 'TlsOptions'.
            Types of property 'pskCallback' are incompatible.
              Type '((hint: string | null) => PSKCallbackNegotation | null) | undefined' is not assignable to type '((socket: TLSSocket, identity: string) => Uint8Array | DataView | Uint8ClampedArray | Uint16Array | Uint32Array | ... 5 more ... | null) | undefined'.
                Type '(hint: string | null) => PSKCallbackNegotation | null' is not assignable to type '(socket: TLSSocket, identity: string) => Uint8Array | DataView | Uint8ClampedArray | Uint16Array | Uint32Array | ... 5 more ... | null'.
                  Types of parameters 'hint' and 'socket' are incompatible.
                    Type 'TLSSocket' is not assignable to type 'string'.

[littlewhywhat]

hey, @brandonchinn178 thank you for this PR! In general LGTM 👍

do you think you can rebase it on the latest master and run npm run build from the root and fix any errors that are shown there? at the moment the build fails. Thank you 🙏 If you don't have time for that please let me know.

@Shinigami92 just to check, you don't see any potential problems here? wondering why this PR stayed here for a year...

[Shinigami92]

ClientConfig from pg defines password as string | (() => string | Promise<string>)
This wont bring a breaking change into the project, but we may need to check if we need to support the non-string callback type

[brandonchinn178]

@littlewhywhat @Shinigami92 Made all requested changes