refactor: disabled pagerduty option due to a design limitation on Bac…

…kstage (#127)

### Description

This PR disables PagerDuty option on service dependency syncing
configuration in `PagerDutyPage`. There is a design option on Backstage
that prevents us to fully replace or remove existing relations from an
entity configuration file. For that reason we are not able to guarantee
that proper behaviour of PagerDuty syncing to Backstage.

Users can still choose to have Backstage as a main source, ou to use
both Backstage and PagerDuty which will merge the two sets of service
dependencies in both platforms and keep them in sync.

**Issue number:** N/A

### Type of change

- [ ] New feature (non-breaking change which adds functionality)
- [x] Fix (non-breaking change which fixes an issue)
- [ ] Breaking change (fix or feature that would cause existing
functionality to not work as expected)

### Checklist

- [x] I have performed a self-review of this change
- [x] Changes have been tested
- [ ] Changes are documented
- [x] Changes generate *no new warnings*
- [x] PR title follows [conventional commit
semantics](https://www.conventionalcommits.org/en/v1.0.0/)

If this is a breaking change 👇

- [ ] I have documented the migration process
- [ ] I have implemented necessary warnings (if it can live side by
side)

## Acknowledgement

By submitting this pull request, I confirm that you can use, modify,
copy, and redistribute this contribution, under the terms of your
choice.

**Disclaimer:** We value your time and bandwidth. As such, any pull
requests created on non-triaged issues might not be successful.

src/components/PagerDutyPage/index.tsx

@@ -132,6 +132,7 @@ export const PagerDutyPage = () => {
                       value="pagerduty"
                       control={<Radio />}
                       label="PagerDuty"
+                      disabled
                     />
                     <FormControlLabel
                       value="both"