Improve display of build targets

[trz42]

Shortens the list of "build targets" (architectures and repository ids). This is shown when a PR is opened or for the command bot: show_config. Tested in https://github.com/trz42/software-layer/pull/72

Example:

Old display

Instance dev-PR254 is configured to build:

• arch x86_64/amd/zen2 for repo nessi-2022.11-swl-deb10
• arch x86_64/amd/zen2 for repo nessi-2023.06-cl
• arch x86_64/amd/zen2 for repo nessi-2023.06-swl-deb10
• arch x86_64/amd/zen2 for repo nessi-2023.06-swl-deb11
• arch aarch64/generic for repo nessi-2022.11-swl-deb10
• arch aarch64/generic for repo nessi-2023.06-cl
• arch aarch64/generic for repo nessi-2023.06-swl-deb10
• arch aarch64/generic for repo nessi-2023.06-swl-deb11
• arch aarch64/thunderx2 for repo nessi-2022.11-swl-deb10
• arch aarch64/thunderx2 for repo nessi-2023.06-cl
• arch aarch64/thunderx2 for repo nessi-2023.06-swl-deb10
• arch aarch64/thunderx2 for repo nessi-2023.06-swl-deb11

New display

Instance dev-PR254 is configured to build for:

• architectures: x86_64/amd/zen2, aarch64/generic, aarch64/thunderx2
• repositories: nessi-2023.06-cl, nessi-2023.06-swl-deb11, nessi-2023.06-swl-deb10, nessi-2022.11-swl-deb10

[trz42]

Most instances will be running on sites where the same architectures are relevant for all repos. This doesn't necessarily have to be the case (e.g. map of zen2 and zen3 for repo A and only zen2 in repo B) and in those cases that distinction is lost with the new reporting (unless I'm missing something). This new conciseness is much better than the previous bullet list, but maybe in a future iteration it might be nice to use a "drop-down on click" approach, or have something like

• zen3 - repoA, repoB
• zen2 - repoB

That's a nice idea. (Thought about that too, but then was too lazy to implement it in the first iteration.)

[boegel]

I agree with Pedro's feedback, why not simply do something like:

Instance dev-PR254 is configured to build:

<details>
...
</details>

[trz42]

I agree with Pedro's feedback, why not simply do something like:

Instance dev-PR254 is configured to build:

<details>
...
</details>

Sure. Another option would be

Instance dev-PR254 is configured to build: (click for details)

- `zen3` - `repoA`, `repoB` - `zen2` - `repoB`

Little downside is that you have to click to see it.

Anyhow everyone can make a PR for an improvement.