use `tokio-postgres` in `outbound-pg` (fermyon#779)

* use `tokio-postgres` in `outbound-pg`

Since `postgres` just wraps the async `tokio-postgres` library in a synchronous
wrapper, and `outbound-pg` exports async methods, it makes more sense to use
`tokio-postgres` directly.

Addresses fermyon#776.

Signed-off-by: Joel Dice <joel.dice@fermyon.com>

* fix PgError mapping

Signed-off-by: Joel Dice <joel.dice@fermyon.com>

Signed-off-by: Joel Dice <joel.dice@fermyon.com>

Merge pull request fermyon#734 from vdice/chore/0.5.0-bumps

chore(*): bumps for forthcoming 0.5.0 release

Merge pull request fermyon#737 from vdice/chore/update-templates

chore(*): update templates and examples to use the v0.5.0 sdk

Merge pull request fermyon#734 from vdice/chore/0.5.0-bumps

chore(*): bumps for forthcoming 0.5.0 release

Merge pull request fermyon#627 from lann/v0.4.0-bumps

chore(*): v0.4.0 pre-release bumps

Merge pull request fermyon#635 from lann/update-templates-v0.4.0

Update templates v0.4.0

Merge pull request fermyon#627 from lann/v0.4.0-bumps

chore(*): v0.4.0 pre-release bumps

Merge pull request fermyon#585 from vdice/chore/v0.3.0-bumps

chore(*): v0.3.0 pre-release bumps

Merge pull request fermyon#588 from itowlson/sdks-to-0.3.0

Update templates to 0.3 SDKs

Merge pull request fermyon#585 from vdice/chore/v0.3.0-bumps

chore(*): v0.3.0 pre-release bumps