docs: Improve PR template guidance

[sentry-junior]

Update the PR template to prompt authors for optional screenshots in the description and a Sentry link in testing details when applicable. This keeps the template concise while making useful review evidence easier to provide.

Validation: git diff --check passed. The required Gradle formatting/API task could not run because Java is unavailable in the sandbox.

Requested by roman via Junior.

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View Junior Session in Sentry

[sentry]

📲 Install Builds

Android

🔗 App Name	App ID	Version	Configuration
SDK Size	io.sentry.tests.size	8.48.0 (1)	release

⚙️ sentry-android Build Distribution Settings

[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	312.50 ms	369.31 ms	56.81 ms
Size	0 B	0 B	0 B

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
6b019b7	319.84 ms	333.15 ms	13.31 ms
eb95ded	317.51 ms	369.08 ms	51.57 ms
319f256	317.53 ms	370.83 ms	53.29 ms
b3d8889	420.46 ms	453.71 ms	33.26 ms
6b019b7	403.90 ms	546.09 ms	142.19 ms
889ecea	367.58 ms	437.52 ms	69.94 ms
d15471f	303.49 ms	439.08 ms	135.59 ms
d364ace	384.53 ms	453.51 ms	68.98 ms
6ea4329	309.06 ms	353.48 ms	44.42 ms
c8125f3	383.82 ms	441.66 ms	57.84 ms

App size

Revision	Plain	With Sentry	Diff
6b019b7	0 B	0 B	0 B
eb95ded	0 B	0 B	0 B
319f256	1.58 MiB	2.19 MiB	619.79 KiB
b3d8889	1.58 MiB	2.10 MiB	535.07 KiB
6b019b7	0 B	0 B	0 B
889ecea	1.58 MiB	2.11 MiB	539.75 KiB
d15471f	1.58 MiB	2.13 MiB	559.54 KiB
d364ace	1.58 MiB	2.11 MiB	539.75 KiB
6ea4329	1.58 MiB	2.29 MiB	719.82 KiB
c8125f3	1.58 MiB	2.10 MiB	532.32 KiB